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ANIMAL MECHANISM

Afy^^d

AND

PHYSIOLOGY;

BEING A PLAIN AND FAMILIAR EXPOSITION OF THE STRUC- TURE AND FUNCTIONS OF

THE HUMAN SYSTEM.

DESIGNED FOU THE USE OF FAMILIES AND SCHOOLS.

• I ,~ ■■ •

BY JOHN H.'^GRISCOM, M.D.,

S>ROFESSOR OF CHEMISTRY tk THE NEW-YORK COLLEGE OF PHARMACY, AND LECTURER ON ANIMAL MECH- ANISM AND PHYSIOLOGY.

"For shall the work say of him that made it, He made me not? or «hall ihe thing framed say of him that framed it, He had no understand- ing ?" — Isaiah xxix., 16.

ILLUSTRATED BY NUMEROUS WOODCUTS BY BUTLER.

NEW-YORK:

HARPER & BROTHERS, 82 CLIFF-STREET,

1839.

Entered, according to Act of Congress, in the year 1839, by

Harper & Brothers, In the Clerk^s Office of the Southern District of New- York,

doll.

PREFACE.

The term Animal Mechanism^ in the title of this work, is substituted for Anatomy^ as pointing more particularly to the mode in which the structure of the human body is described, and not as indicating any difference in the objects themselves, from those which are usually considered under the lat- ter head. For the purpose of making the study of anatomy more easy and agreeable, the human frame is considered, in the following pages, as a machine^ composed of apparatus of various kinds, adjusted to each other in a surpassingly ingenious manner, carrying on their apparently incongruous operations without interruption from each other, and all working together for the attainment of the one great end for which the machine was devised with the most perfect harmony.

This view of the subject cannot justly be con- sidered to derogate from the exalted interest which the contemplation of this last and noblest work of the Creator should always inspire. Apart from the fact that the animal structure can be shown to be a combination of implements acting upon well- known philosophical and mechanical principles, bringing to its aid the sciences of Chemistry, Hy- draulics, Hydrostatics, Pneumatics, Mechanics,

]| PREFACE.

Optics, and Acoustics, this manner of exhibiting its different departments proves it incontrovertibly to be the work of premeditation, inasmuch as con- trivance and design are demonstrable in each part of the machine.

Anatomy, as it is usually taught in schools and in books, is simply a description of the various tis- sues of the body, taken up one by one, the use of each being pointed out conjointly with its descrip- tion. To the general student, the subject is thus deprived of much of its interest, and the study itself is rendered more tedious and irksome ; while the contemplation of the various organizations in their mutual dependencies, and the perfection of their relations, is in a great degree lost or obscured.

It is, therefore, in connexion with the objects for which they have been created, that the various or- gans of the human frame are described in this work ; in other words, the nature of the function being explained, the apparatus employed to effect it is described, so that its applicability to the pur- pose is at once seen.

To exhibit in a clear light the ingenuity which has been employed in the construction of this won- derful fabric, comparisons have in some instances been instituted between these works and those of art, and the examination may be safely committed to any one who will undertake it in the spirit of candour and truth.

Occasion is taken, also, to compare the con- struction of individual organs of the human frame with the corresponding organs of inferior animals ; by this means a more just conception may be ob- tained of the wisdom displayed in the human fab-

PREFACE. Ill

ric, adapted, as it must be, to the superior intelli- gence and more elevated rank of man. Every an- imal is, indeed, perfectly adapted, by its formation, to the sphere in which it was intended by nature to live and move ; and if any apparent defect exists, it is safe to conclude that what we should presume a nearer approach to perfection would, in fact, be an unnecessary refinement, if not a positive incon- venience.

In alluding to those supposed defects of organi- zation in some of the lower animals, with regard, for example, to the sloth, and others of the Tardi- grade species, which are remarkable for the slug- gishness of their movements, the author of '' the Hand," one of the Bridgewater Treatises, makes the following just remarks :

" Modern travellers express their pity for these animals : while other quadrupeds, they say, range in boundless wilds, the sloth hangs suspended by his strong arms ; a poor, ill-formed creature, defi- cient as well as deformed, his hind legs too short, and his hair like withered grass ; his looks, mo- tions, and cries conspire to excite pity ; and, as if this were not enough, they say that his moaning makes the tiger relent and turn away* This is not a true picture: the sloth cannot walk like quadrupeds, but he stretches out his strong arms, and if he can hook on his claws to the inequalities of the ground, he drags himself along. This is the condition which authorizes such an expression as * the bungled and faulty composition of the sloth.' But when he reaches the branch or the rough bark of a tree, his progress is rapid ; he climbs hand over head along the branches till they

A2

Vf PKET'ACE.

touch, and thus from bough to bough, and from tree' to tree ; he is most alive in the storm ; and when the wind blows, and the trees stoop, and the branches wa^e and meet, he is then upon the march."

Anatomy is that science which teaches us the structure of animal bodies.

Physiology unfolds to us the nature of the dif- ferent parts, and of the functions which they per- form.

The latter science consequently depends much for its elucidation upon its sister science chem- istry.

The chemist knows that it is by the combina- tion, in different proportions and quantities, of a comparatively few simple elements, that the great number of natural bodies is formed ; so, likewise, the anatomist can show that the various structures of animal bodies are composed of a few original elementary tissues.

The number of these tissues^ whose varied com- binations form all the organs of animal bodies, has been reduced to the following short list ?

1. Cellular.

2. Adipose or medullaryr

3. Vascular. .J 4. Nervous.

5. Osseous.

6. Fibrous.

7. Cartilaginous.

8. Fibro-Cartilaginou&r

9. Muscular.

10. Spongy.

11. Mucous*

PREFACE. T

12. Serous.

13. Dermoid, or Skin.

14. Gfendular, as Liver, Kidneys, &c.

Some of the organs consist of only one of these tissues, while others are compounded of two or more of them in various proportions. We speak now of the solid parts of the animal structure, the fluids, which constitute a large part of the bulk of the body, not being enumerated in the foregoing list. Those fluids which are concerned wholly or in part in the formation of the body, are,

1. The Blood.

2. The Gastric Juice.

3. The Saliva.

4. The Bile.

5. The Pancreatic Juice.

6. The Optic Humours.

Besides these, we find a few which, though more abundant in quantity than some of the preceding, must be ranked as excretions, and not looked upon as essential to the system ; these are,

1. The Perspiration,

2. The Urine.

3. The Tears.

As far as modern researches in chemistry have extended, the fact has been developed that there are but fifty-four elementary substances, by whose varied combinations all the materials of the uni- verse are composed.

The immense varieties of matter known to us are chemically distinguished from each other chiefly by their composition.

In the inorganic world we find all the elements or jsimple substances of the chemist ; but in or-

Vi PEEFACE.

ganic nature the case is very different. All vege- table and animal bodies are composed in general of a few elements, and differ in chemical composition but by slight variations in the number, proportions, and juxtaposition of their combining elements.

The simple substances which are found to con- stitute the great bulk of animal matter, are Oxy- gen^ Hydrogen, Carbon, and Nitrogen. A few of the other elements are found to give a character to some specific substances. Thus the bones con- tain phosphorus and lime, the blood iron, &c. So, also, some animals contain some substances in some part of their structure, by which they are distinguished from all other creatures.

The functions which are considered in this vol- ume are those of,

1st, Circulation.

2d, Respiration.

3d, Speech.

4th, Secretion.

5th, Muscular Actioti.

6th, Nervous Action.

7th, Digestion ; and,

8th, Those of the Osseous System, the latter being alluded to only as its different parts relate to, and are connected with, the other functions. The study of the bones, although presenting as many points of interest as any other, has generally been considered as dry as the subjects themselves, even to those who are especially interested in the ac- quisition of anatomical knowledge. It could not be expected, therefore, under the old mode of treat- ing the subject, even in popular works, that the general student would find the study sufficiently in-

PREFACE. Vll

teresting to enable him to peruse it without tedium or perhaps dislike.

To divest this interesting branch of knowledge of its repuTsiveness, and to render it more easy and attractive, has been the object of every attempt at popular physiology. And a wish to contribute something that may render the knowledge of the structure of our frames more ofeneral amoncr non- professional people, is the author's inducement for submitting this little work to the public. How far it may prove to be a vdrable addition to those al- ready known, can be determined only by lime and experience. One prom^.-ent motive, he is free to confess, has been the desire to render the study of our frames subservient to moral improvement, by furnishing the young reader with incontestible ev- idence of a Great First Cause. This, he is aware, is treading in a path over w^hich many brilliant minds have gone before, and it may seem pre- sumption in him even to follow them.

With all proper deference, however, to their valued productions, it is his impression that no work has yet come to his knowledge which exclu- sively, and with sufficient amplitude and freedom from technicalities, treats of the mechanism of the human bodv, either with or without reference to this great point, with that simplicity which is needful for general readers and common schools.

The arrangement of the subjects treated of in this work, he apprehends, is new ; but the peculiar mode of teaching them is, with some variations, that which has been so successful in the hands of Sir Charles Bell, Dr. Arnott, and a few other mod- ern writers. The plan has been more fully car-

Vlli PREFACE.

ried out than in any single work that the author has met with, and he hopes that this little book may be productive of some (if not as much) of the good fruits which have followed the plantings of others in this field of popular knowledge.

Without the aid of that book which leads to a still closer acquaintance with the author and finisher of this magnificent universe, these studies are a suf- ficient proof of the existence of an Omnipotent De- signer ; for that wisdom must be almighty that could adapt such apparently incongruous ends to each other, and blend into one harmonious whole the millions of different ranks in the great scale. Nor only this ; it proves that one mind alone has conceived, and one hand executed and perfected, the great and incomprehensible work of the uni- verse ; the singleness of an individual power could alone produce it ; no division of mind could have accomplished it. We are therefore impelled to the conclusion, that the Power which created the heavens ; " which maketh Arcturus, Orion, and Pleiades, and the chambers of the South ;" the earth, and all that is therein ; even man, the most perfect and complex of all created beings, is one in all his manifestations.

CONTENTS.

CHAPTER I.

CIRCULATING APPARATUS.

Waterworks of a City— Of Philadelphia — Analogous Vessels of Animal Bodies — Heart, Arteries, Veins, and Lungs. — The Heart. Its Situation — Double and Single— Two Sides— Auri- cles and Ventricles— Course of the Blood through it— Motions of Anricles simultaneous— Do. Ventricles— Their Action illus- trated by Bellows— Valves — Tendinous Cords — Muscular at- tachment of Cords — Aortic Valves — Illustrated by common Pump— Size of Heart — Number of its Pulsations — An invol- untary Muscle. — The Bloodvessels. Difference between them and Water-pipes — Between Arteries and Veins — Means of distinguishing them. — Capillary System. Its Situation — Ob- jects—Extent— Inflammation. — Causes of Blood's Progression. Heart alone insufiicient — Construction of the Vessels— Vari- ations Page 13

CHAPTER n.

RESPIRATORY APPARATUS.

Colour and Properties of Arterial and Venous Blood— Former Red— Latter Black— Change produced in the Capillaries — Lungs — Purification of Blood, how effected — Air Cells — Trachea— Its Branches— Compared to a Tree — Three great Cavities of the Body— Chest— Boundaries — Ribs— Diaphragm — Intercostal Muscles — How does Air get into the Chest? — Action of Bellows — Enlargement of Chest, how made— Ac- tion of Diaphragm — Air enters the Lungs— Respiration the Source of Animal Heat— Constitution of the Air— Changed by Breathing — injurious Effects of bad Air— and imperfect De- velopment of fc) best— Formation of Aqueous Vapour — Devel- opment of Caloric 43

CONTENTS.

CHAPTER III.

VOCAL APPARATUS.

Organs of Voice — Comparison with Musical Instruments — Wind-pipe — Rings — Larynx — Chink — Vocal Ligaments — Valve— Effects of Foreign Bodies in the Trachea— Coughing

Page 71

CHAPTER IV.

THE BLOOD

Holds in Solution all the Materials of the Body. — Physical Properties: Colour; Consistence — Coagulation — Crassamen- tum — Serum — Fibrin : Temperature ; Quantity ; Weight. — Chemical Properties, vital Properties, Secretion —Vital Principle 75

CHAPTER V.

motory apparatus. — Part 1st.

Motion— Locomotion. — Muscle — Its Structure— Body — Inser- tion— Origin — Circular Muscles — Pulley — Muscles of the Eye — Every Motion in the Body the result of Muscular Contrac- tion— Number of iVIuscles— Mode of Action — Voluntary and Involuntary — Velocity — Tenacity — Means of Attachment — Tendon. — Levers, 1st, 2d, and 3(i Kinds— Instances of each — Their Advantages 91

CHAPTER VI.

motohy apparatus, — Part 2d.

Bones and Joints. Skeleton — Constitution of Bone — Shape. OP Bones — Joints. Six Varieties— Means to prevent Wear and Friction — Internal Structure of Bone— Hinge Joint — Friction Wheels — Toggle Joint 122

CHAPTER VIL

physiology and effects of exercise.

Resemblance between Globule of Blood and of Muscular Fibre —Bulk of Muscles— Extent of the Influence of Active Circu- lation—Its Effects— Instances— Exercise must be Uniform and not Excessive— Fatigue— Inaction weakens Muscles — Eflfects of Tight Dressing on the Spine ... 162

CONTENTS. XI

CHAPTER VIII.

THE HAND.

Superiority— WJjole upper Extremity to be Studied— Descrip. tionot'theUpper Extremity— Shoulder Blade— Collar Bone— Humerus— Shoulder Joint— Ulna and Radius— Elbow Joint —Wrist Joint— Joints of the Fingers— How Moved—THE Thumb— Organ of Touch— Nails - - - Page 174

CHAPTER IX.

THE SKIN.

Three Layers— Its Elasticity— Its Transpiring Power — Experiments of Dr. S. Smith— Its Absorbing Power— Its Sensibility 198

CHAPTER X.

the nervous system.

Consists of four Principal Parts— The Brain — Spinal Cord — Nerves — Spinal Irritation. The Muscular Sense— Sym- pathetic Nerve - - - - - - - 215

CHAPTER XI. protection afforded to the brain and spinal marrow.

Two Modes of Injuring the Brain — Description of the Scull — Its Arch — Dovetailing— Arch of the Foot — Proper Mode of Walking — The Lowet Extremities — The Spine — Vertebrae — In- tervertebral Substance— Harmony of Organization and Oper- ation 245

CHAPTER XII.

the *' packing" op the body.

Cellular Tissue— Fat — Its Elasticity — Utility— Diseases to which it is liable 270

CHAPTER XIII. digestive apparatus.

Regeneration of the Blood— Enumeration of different Organs- Teeth— QE sophag us— S tomach— N ervous Influence— Duode-

B

XU CONTENTS.

num — Theories of Digestion — Gastric Juice—Chyme— Liver — Pancreas — Chyle^ — Lacteals — Thoracic Duct — Case of Alexis St. Martin— Dr. Beaumont's Inferences - Page 278

CHAPTER XIV.

THE SENSES.

Organic and Animal Life — Senses the Sources of Enjoyment and Protection. — The Eye — Sclerotic Coat — Cornea — Retina — Choroid Coat— Humours of the Eye — Aqueous Humour— Iris — Crystalline Lens — Vitreous Humour — Nature of Light — Protections of the Eye— Orbit— Curtains of the Eye — Eyelids — Tears — Lachrymal Gland— Eyebrows — The Ear — Sound — The External Ear — Tube of Ear — Tympanum — Bones of the Ear — Internal Ear. — The Nose. — The Tongue as the Organ of Taste - * . . -315

Several selections will be found in this work from the pages of other authors, but it has not been deemed necessary to specify at each quotation the book from which it is taken ; a general acknowledgment, it is presumed, will be sufficient. It is be- lieved that no quotation has been given without its being indi- cated by the usual typographical marks.

The following list comprises the works from which extracts have been made : numerous others have been consulted.

Arnott's Elements of Physics. — Beaumont's Experiments on Digestion.— Bell on " The Hand."— Bell and Brougham's Illus- trations of Paley. — Bostock's Physiology. — Combe's Physiology. -^Dunglison's Physiology. — Family Magazine. — Horner's Anat- omy.— Library of Useful Knowledge. — Medico-Chirurgical Re- view.

ANIMAL MECHANISM

AND

PHYSIOLOGY.

CHAPTER I.

CIRCULATING APPARATUS.

1. There are to be found in many large cities, as New-York, Philadelphia, and London, arrange- ments for supplying them plentifully with water, to be used by the inhabitants for the various purposes of drinking, bathing, extinguishing fires, cleansing the streets and houses, &;c. This supply is fur- nished by means of an extensive apparatus, com- posed of, 1st, A basin elevated above the tops of the houses, as on a hill, or on a place built purposely for it, into which basin the water is forced by a waterwheel or a steam-engine ; 2d, Of a large pipe running from the bottom of this basin towards the city, under ground ; and, 3d, Of an arrange- ment of smaller pipes leading from the large one, which, by dividing and subdividing, serve to con- vey the water, not only into every street, but into every lane, every alley, every house, and every room in the house, where, by turning a stopper, any person can obtain a full supply of this neces- sary fluid.

14 CIRCULATING APPARATUS.

One of the most simple and economical arrange- ments for this important purpose is to be found in Philadelphia. The water of the Schuylkill River, which is there used, is, by an ingenious yet very simple contrivance of waterwheels and for- cing-pumps, made to raise itself to the basin on the top of a high mound, whence it circulates through many miles of pipe, and unnumbered ramifications, into every corner of that large city. Not the least beautiful part of this arrangement is, that the stream, as it flows along, keeps in motion the ap- paratus which raises the water of the same river to the basin. So that, supposing the machinery to be always in order, as long as the river continues to run, so long will the city be copiously supplied with the healthful fluid, requiring only the care of one man to regulate the quantity in the reservoir,

2. Besides this apparatus of pipes just described, the houses and streets of the cities are farther sup- plied with an arrangement of channels and sluices for the purpose of conveying away the water which has been used, called "waste water." To this end we find each house furnished with a " waste pipe," which empties into a channel in the alley of the house ; this channel empties into the gutter of the street ; several of these unite to form larger gutters, and the latter continue on to a " sewer" under ground, which collects the water from all the large gutters on the surface, and conveys it to the river whence it came, but emptying into it at a point at a distance below the waterworks, that the pure water may not be contaminated.

3. The impure water, after being thrown back into the river, is, by the heat of the sun and other

CIRCULATING APPARATUS. 15

causes, evaporated, the impurities being left behind ; and the vapour, being Hghter than the air, rises high above the earth, and is there condensed, form- ing clouds, which after a while empty themselves upon the eartR in the form of rain, which runs into the river. The water is thus purified and render- ed fit for use again. So, if we could suppose the Schuylkill the only river anywhere near Philadel- phia, and the supply from the clouds sufficient for the purpose, the inhabitants of that city would use the same water over and over again an indefinite number of times.

4. There is in the human body a circulating ap- paratus very analogous to this in many particu- lars. It is for the purpose of carrying through the system a peculiar and very important fluid, the Blood ; the circulation of which is the principal means whereby the body is made to grow in size and strength, and by which fresh material is de- posited in the place of the old, which has worn out or otherwise become Unfit for use.

5. Like the apparatus which supplies a city with good water, that which supplies the animal body with blood is composed of several distinct parts.

There is, first, a powerful and complicated ma- chine, which receives the blood into its cavities, and then acting upon it like a forcing-pump, pro- pels it into the

Second part of the apparatus, which consists of a very extensive series of tubes or pipes, through which the blood is conveyed to all parts of the body, to give it nourishment and health, and to take up the decayed and unhealthy particles.

The third part consists of another set of pipes,

B2

16 CIRCULATING APPARATUS.

which collects all the blood after it has been used and has become impure, in order to return it to a part of the body where it may be renewed, and made fit to nourish the body again.

In the last place, the impure blood undergoes the process of purification, by which it is completely restored to its healthy state, being deprived of all its noxious properties, and, like the water from the clouds, is again good for use. It is then put back into the first machine, and again sent through the proper pipes all over the system,

6. The machine which, in the animal body, is used to force the blood into the pipes, is the Heart,

The first set of tubes, which receive the blood immediately from the heart, are called Arteries, These carry the fluid through the whole system, and it passes from them, after being used, into the next set of vessels, called Veins, which carry it back.

The organs in which the blood is purified are called Lungs, and from them it is returned to the heart, to be recirculated through the same channels.

7. The following are, then, the organs concerned in the transmission and purification of the blood, viz., the heart, arteries, veins, and lungs. All of these organs, but especially the first, are very beautiful and complicated in their structure, and are worthy a minute acquaintance.

OF THE HEART.

8. The heart is situated in the chest, behind the breast-bone, and its motion may be felt by the hand when placed on the left breast. It is of about the size, in the adult, of a man's fist, and is com-

CrKCULATING APPARATUS.

17

Fig. 1.

EA.

The Heart, as it appears when isolated from all surrounding

parts.

f.osed almost entirely of strong muscular fibres, ts shape is conical, and it is situated with the apex pointing downward and to the left side, while the base is above and towards the right side.

9. All animals which breathe atmospheric air have hearts divided inside into^bwr chambers, sep- arated from each other by strong muscular walls. In those animals which do not breathe, as fishes, the heart has only two cavities. Breathing ani- mals have, therefore, double hearts, and non-breath- ing animals have single hearts.

In breathing animals one half the heart is for the purpose of propelling the blood into the lungs, there to be purified ; and the other half is for sending the blood through the arteries into the

18 CIRCULATING APPARATtTS.

body. When it returns through the veins, there- fore, it empties into one part of the heart, and thence is sent to the lungs.

Non-breathing animals having no lungs, a single heart only is required. Their blood is purified in another manner.

10. Double hearts are divided anatomically into two sides, the right and left, each having two cav- ities. The right side receives the blood from the veins, and sends it into the lungs ; the left side re- ceives it from the lungs, and sends it through the body.

'"^ Fig. 2.

These cavities are called auricles* and ventri-

* Derived from auricula (Latin), an ear; from its resem- Dlance in shape to a dog's ear.

^,. Jli^^ .{ai^M^.^ « . !»: M.

CmCULATING APPARATUS. 19

cles.* In the right side there is one auricle and one ventricle, and one of each also in the left side.

This diagram (fig. 2) shows the relative situation of these four cavities. The blood enters the heart from the great veins V. V. These throw it into the right auricle R. A. Thence it goes into the right ventricle R. V. ; and from that cavity into the lungs, through a bloodvessel called pulmonary artery, P. a. After being purified, it returns to the heart through another bloodvessel, the pul- monary vein, P. v., which empties into the left au- ricle L. A., and that empties itself into the left ventricle L. V. From this last cavity it is sent to the body through the main pipe A., called Aortay which is the largest artery in the system.

11. When the right auricle has become filled with the blood from the veins, its sides, which are formed of strong muscular fibres, contract upon it, and thus reduce the dimensions of the cavity, by which means the blood is forced into the adjacent ventricle. The ventricle consequently becomes distended ; and when it is filled, its walls, which are stronger than those of the auricle, on account of its having to send the blood farther, also contract, and force the blood through the pulmonary artery into the lungs.

When the blood returns from the lungs to the left side of the heart, the contractions and dilata- tions there correspond exactly with those of the right side.

The auricles expand together, and contract also at the same moment.

♦ From ventriculus (Latin), a stomach ; from its fancied re- semblance to a stomach in form.

20 CIRCULATING APPARATUS.

The ventricles are likewise simultaneous in their imovements.

12. Each auricle and each ventricle has, of course, two openings, one for the entrance and the other for the exit of the blood. By reference to the preceding diagram, it will be seen that the two openings in each ventricle are equally in the di- rection of the current, when the ventricle contracts upon the blood to expel it. Were it not for a wise and most beautiful provision, the blood would be as likely to return to the auricle as to go out the proper way.

A pair of common bellows will illustrate this. It has two openings, one through the nozzle, and the other, much larger, in one of the boards. When the boards are pulled apart, the air enters through the latter hole ; and wiien they are forced together, the air would pass as rapidly out through the same opening as it entered, were it not pre- vented. This is done by a leather flap or valve, which covers the opening inside, and the air is consequently all forced out through the nozzle, the place designed.

The action of each ventricle is precisely analo- gous to that of the bellows, the blood being pre- vented from going back into the auricle by an ar- rangement of delicate little valves represented in the annexed cut (fig, 3).

13. These valves are three in number in the right, and two in the left ventricle, and are made of exceedingly fine membrane, of a peculiar tex- ture, so thin as to be translucent, yet strong enough to sustain the whole power of the ventricle. Their shape is somewhat triangular, and similar to that

CIRCULATING APPARATtTS.

21

of the moon when gibbous, or about three quarters full. The opening between the two cavities is nearly circular, and about one inch in diameter. The valves are attached by one edge to the inside of the opening very firmly, while the other edge is loose, and flCiats backward and forward as the blood moves it.

14. When the right auricle contracts, the blood is pushed against the valves, which give way and allow it to pass ; but when the ventricle contracts,

Fig. 3.

1

Right side of the heart, laid open to show the valves. V. C, V. C, the great veins bringing the blood to the heart. R. A., the right auricle. R. V., the right ventricle. Between the two are seen the valves V. V., and to them are attached the tendi- nous cords which are fastened by muscular fibres /. I. to the in- side of the ventricle, '

"22 CIRCULATING APPARATUS.

the blood is forced against the opposite sides of the valves, and pushes them to, like little doors. They fall against each other, and completely close the opening so as entirely to prevent the blood from going back into the auricle.

15. But the valves could not, unaided, withstand the current against them, and would themselves be forced into the auricle, were it not for a guard with which they are most effectually furnished.

16. This consists of a number of extremely small, delicate, silk-like cords, made of fine tendon, which are fastened by one end to the loose edges of the valves, and by the other end to the wall of the ventri- cle inside, and directly opposite the opening from the auricle (figure 3). These fine cords run, there, fore, immediately across the cavity of the ventri- cle ; they are very flexible and strong, and are just long enough, when the ventricle is distended, to allow the valves to lie flat and cover the opening completely ; and short enough to prevent them be- ing pushed through into the auricle. They act very much like the ropes attached to the corners of the jib sails of a ship, which keep the sails from being blown away by the wind. The ropes have no contractility, and hold the sail merely by their strength ; the cords of the valves are equally de- void of contractility, and, though v.ery fine, are pos- sessed of great strength. |

17. But this is not all the beauty and ingenu- ity of this wonderful and delicate mechanism, j These tendinous cords are of exactly the requi- site length, when the ventricle is fully expand- ed, to keep the valves in their proper places. But when the ventricle contracts, and its sides are

CIRCULATING APPARATUS, 23

brought nearer to each other, it is apparent that the cords must become loosened, and the valves be allowed to float into the auricle, and thus destroy their use as valves, without some preventive against such an accident. Such a preventive is beautifully provided. The cords are attached to the ventricle by the intervention of little muscles (Z. Z*, fig. 3), which contract at the moment the ventricle con- tracts, in an opposite direction, and just enough to keep the cords always at the same degree of ten- sion. When the ventricle expands, these muscles relax in a corresponding degree, so as to elongate the cords and accommodate them to the varying diameter of the ventricle.

The action of the valvular apparatus in the left side of the heart corresponds precisely with that of the right side, except that there are but two valves in the former instead of three, as in the latter (fig, 4).

18. There is still another kind of valvular ac- tion in the operations of this curious and interest- ing organ, much simpler, but equally efficacious with the last, which is very similar in principle to that found in tl^^ common pump. In the tube of this useful instruraent there is a fixed block, with a hole through it, fajLtened to which is a valve of leather, which opens upward and allows the water to ascend freely througb it. But the instant the water begins to descend, the valve falls down over the hole in the block, stotpping it up completely, where it is kept by the weight of the water above, and prevents its descent. Another valve, precisely similar to this in its make aud action, is attached

C

24

CIRCULATING APPARATUS.

Fig. 4.

Left side of the heart, with the valves. R. A. awd R. V., the right auricle and ventricle. P. A., the pulmaiary artery, cut off near its origin, to show the aorta, A. a. L. V., the left ventricle. L. A., the left auricle. V. is between the valves which command the opening between the aur^^'Ie and ventricle. A. is the mouth of the aorta, with its valves tereafter described. t. e.j branches of the pulmonary artery.

to a block which moves up ar<i down in the pump with the piston-rod, /

19. In each of the two great arteries which carry blood from the hear/ (one from the right ven- tricle to the lungs, the ot^er from the left ventricle to the body), is found ap admirable arrangement of valves acting on principles precisely similar. A description of one will suffice for both.

The aorta, or main artery of the body (A, a«)

CIRCULATING APPARATUS.

25

fig. 4), is about one inch in diameter, and as it rises from the left ventricle, ascends perpendicu- larly about three inches before it makes a curve to descend. When the ventricle contracts, the blood is forced into the aorta, which becomes filled ; and the moment the ventricle begins to expand, the blood in the aorta begins to fall, and would inevit- ably return into the cavity, were its progress not arrested by a set of valves placed at the mouth of the artery (A., fig. 4).

Fig. 5.

v., the upper part of the ventricle, and A., the aorta, rising from it. At the mouth of the artery are seen profiles of two of the valves, open to admit the blood from the ventricle. At this point the diameter of the arterv is a little larger, to serve the purpose mentioned in the text.

20. " At the root or origin of the aorta, there is a firm ring, to which the valves now to be de- scribed are attached. The necessity of this will appear evident, snice, if the ring could be stretched by the force of the heart's action, the valves or floodgates would not be sufficient to close the pas-

26

CIRCULATING APPARATUS.

sage ; their conjoined diameters would not equal that of the artery which they have to close. These valves are three in number ; they are little half- moon shaped bags of thin membrane, which are thrown up by the blood passing out from the ven- tricle, but by the slightest retrograde movement of the blood their margins are caught, and then, be- ing distended or bagged, they fall together and close the passage.

Fig. 6.

Represents the figure which the three semilunar valves placed at the mouth of the aorta assume when distended by the refluent blood.

" There are some curious little adjuncts to these valves, which ought to be ex})lained, as showing the accuracy of the mechanical provision.

CIRCULATING APPARATUS. 27

" When the margin of the valve is thrown up by the blood passing out of the heart, it is not per- mitted to touch or fall flat upon the side of the artery, for if it did it would not be readily caught up by the blood that flows back ; there is, there- fore, a little dilatation of the coats of the artery, forming a pouch behind each valve, by which, be- ing always full of blood, although the margins of the valve be distended to the full circle, they never cling to the coats. These valves, then, are never permitted to fall against the coats of the artery, and, therefore, they are always prepared to receive the motion of the refluent blood.

" To strengthen the valves, a tendon runs along their margin like the bolt-rope or foot-rope along the edge of a sail, and these tendons are attached to the side of the artery, and give the valve great strength." They effectually secure the valves against being torn at their edges.

21. All the beautiful and intricate apparatus which is here described, and much more not par- ticularly described, it must be recollected, is con- tained in an organ not larger than a large man's fist ; every part of it is, moreover, kept incessantly in motion, from the first dawning of life until the last breath of the individual. If this should pro- duce surprise in any one, how much must that be increased when he is told that the contractions and expansions of the heart, and, of course, the open- ing and shutting of these little valves, take place, on an average, about seventy times in a minute ; and sometimes, in a state of disease, as often as 150 times a minute.

22, The heart belongs to that class of muscles

C2

28 CIRCULATING APPARATUS.

termed involuntary, i. e., not under the control of the will. It is entirely out of our power to cause the heart to stop acting except by mechanical vio- lence. The existence of our lives depends imme- diately upon the action of this organ, for we die the moment it ceases to beat. It is the first to move and the last to die. Seeing its vast impor- tance, is it not a subject for our profound admira- tion that its operations should be placed entirely beyond the reach of our will 1 a will proverbially fickle, uncertain, and treacherous. Had it been made a part of our duty to attend to the regulation and continuance of the minute and complicated ac- tions of this important organ, we should never be able to give our attention for an instant to any other subject ; and " a doubt, a moment's pause of irres* olution, a forgetfulness of a single action at its ap- pointed time, would terminate our existence."

OF THE BLOODVESSELS.

23. Having described the organ which propels the blood into the circulating pipes, these must next be explained. They consist, as already sta- ted (6), of two sets, viz., the Arteries, which carry the blood through the system, and the Veins, which bring it back to the heart. The annexed plates will present a very good general view of both these systems of bloodvessels.

CIRCULATING APPARATUS. Fig. 7.

29

Venous Svstem, or principal veins of the body; t^fJa^SP vein in the centre being the vena cava, into which all the mi- aor veins empty themselves.

so

CIRCULATING APPARATUS.

Arterial System, or principal arteries of the ^ody; the main artery in the centre being the aortA) communicating 'with the heart, where it appears cut off.

CIRCULATING APPARATUS. 31

24. In comparing these bloodvessels with the water-pipes of a city, several striking differences are to bo noticed.

1st, The water-pipes are rigid, firm, inflexible, inelastic tubes. 2d, They cannot be bent without breaking. 3d, They cannot grow larger or small- er, nor alter their position in any way. 4th, They have no power in themselves to propel their con- tents onward, but the v/ater runs through them en- tirely without aid from them. On the contrary, the bloodvessels are, 1st, Soft, very flexible, and very elastic, yet strong. 2d, They can be bent to any extent without danger, as is exemplified in those which run over the joints, and wherever any motion is made in the body. They adapt them- selves readily to any position. 3d, They change in size as the growth of the body requires, and as they have more or less blood to convey. 4th, They have a power in themselves by which they assist in propelling their contents forward.

25. There is considera,ble difference between the structure of the arteries and that of the veins. The former are denser, much thicker and firmer, and much more elastic than the veins, and afford great assistance to the heart in forwarding the blood. The veins are thin, soft, and have little or no elasticity. Many of the veins being very long, and having a high column of blood to hold, as in the leg from the foot to the hip, they are furnished at intervals with little valves, which prevent the blood from flowing back, but allow it to pass up- ward freely ; thus any undue pressure on the del- icate vessels is avoided.

The only valves in the arterial system are those

32 CmCULATING APPARATUS.

already described as at the origin of the aorta and plumonary artery (20).

26. The aorta receives all the purified blood from the heart, and from the aorta arise branches, which run in every direction to supply the various sections of the body. In the little pouch behind the aortic valves are the openings of two small vessels, which supply the substance of the heart with fresh blood. The origin of one of these may be seen in fig. 6. Just at the great curve of this vessel, it gives off two large branches, one to go to each arm ; and two more to supply the head, one going up on each side of the neck. It then descends along the left side of the spine, and as it goes past each rib, it gives a branch to each ; when opposite the stomach it sends a branch to that organ ; so also the liver, the spleen, the bowels, kidneys, blad- der, and all the other organs in this part of tho bodv, receive their blood from this vessel.

When it has descended as far as the lower end of the spine, the aorta terminates by dividing into two branches, called iliacs, one of which goes to- wards each thigh, which, with the leg and foot, it furnishes with blood.

The o-eneral direction of the arterial circulation may be pretty well understood by referring to fig- ure 8. It will be seen there that the arteries of the limbs are composed of one main branch for each, until they arrive at the elbow and knee joints, when they divide into two branches, one running down each bone.

The minute ramifications at the top of tho figure give a slight outline of the circulation of the head and brain.

CIRCULATING APPARATITS. 33

28. The venous circulatioiij with a few differ, ences, follows nearly the same route as the arte- rial. There are about the same number of main branches, but the smaller ramifications appear to be more numerous, as seen in the figure. The direction of the current of blood, of course, is the reverse of that in the arteries, being from the ex- tremities towards the heart.

Through the veins the blood runs in a very dif- ferent manner from what it does through the arte- ries. The former carry it in a regular, uninter- rupted current ; but through the latter it goes along in jets. By placing the finger on the artery at the wrist or on the temple, its action may be felt ; the blood goes along in " pulsations," as they are called, which are simultaneous with the pulsa- tions of the heart ; but in the veins there are no pulsations. When an artery is cut so that the blood can run out of it, it goes out in leaps, jutting at every pulsation several feet, if the vessel is not very small. But when a vein is opened, as in bleeding, the blood runs out in a smooth, even stream.

29. It is more difficult to arrest the bleeding from an artery than from a vein, because the ar- teries are thicker and stouter, and also because they propel the blood with more force. A wound of an artery is, therefore, more dangerous than a wound of a vein.

On this account chiefly we find the two systems placed in different situations in the body and limbs. The larger arteries are placed as far as possible from the surface ; they run along close to the bones, which give them protection, and they are

34 CIRCULATING APPARATUS.

freely covered by thick beds of muscle and tendon. On the other hand, an injury of a vein being less dangerous, they are more exposed. They run along near the surface of the body as well as deep under the skin, and in many places they can be distinctly seen, as on the back of the hand and along the arm. If a string or riband is tied mod- erately tight around the arm above the elbow, the passage of the blood through the veins will be stopped at that point, and below that they will be- come distended with the blood which runs into them. When a physician wishes to bleed a per- son, he ties a ligature around the arm just tight enough to arrest the circulation through the veins, and when they have become distended, he opens one with the lancet, and the blood flows out. He has to be careful not to bind it so tight as to stop the circulation through the arteries of the limb, otherwise he will be unable to draw any blood,

OF THE CAPILLARY SYSTEM.

30. Between the arteries and veins there is an- other system of bloodvessels not yet mentioned. It is called the Capillary System, and derives its name from the minuteness of the vessels, they be- ing as fine and finer than hairs.* These vessels, throughout the whole body, occupy a place, and are the connecting link, between the extremities of the arteries and the commencement of the veins, and transmit the blood from one to the other. Their functions are not less important than those of any other part of the circulating apparatus. It

* From the Latin word capillusy a hair#

CIRCULATING APPARATUS. 35

is a part of their duty to receive from the arteries the pure and healthy blood, to take from it the new material and deposite it in its proper place, and at the same time to take up the worn-out and impure matter of the body and carry it to the veins, to be removed by them from the system.

31. " From the capillaries the peculiar fluids are secreted, the body is nourished, and many other processes are accomplished. Their number is considerably greater where secretion is to be per- formed, than where their object is only the nutri- tion of the part. For this reason, the liver, stom- ach, &;c., which secrete certain fluids that are es- sentially necessary to the system, are supplied with a greater quantity than the bones, ligaments, and skin ; and, indeed, so extensive is their distri- bution, that these important organs seem to be al- most wholly made up of an immense network of capillary vessels.'^ /

32. These being the objects of this set of ves- sels, it will at once be perceived that they must oc- cupy every point of the entire body. Every parti- cle of the body, in process of time, becomes by age and use unfit to be longer employed, and must be removed, and its place supplied by fresh particles. The removal and deposite are eflfected by tba capil- lary vessels alone.

33. Moreover, we know that, from infancy to manhood, the body is daily increasing in size ; the bones grow longer and stouter, the muscles grow larger and stronger, an-d the whole frame becomes in a few years a hundred or more pounds heavier. This is brought about in the following manner : the nutritious portion of our food is converted into blood ; the heart and arteries garry the blood all

D

36 CIRCITLATING APPARATUS.

•

over the body ; the capillaries select the proper par- ticles for each organ from the blood, and deposite it in its right place. We may thus see something of the importance of these little agents ; and the univer- sality of their existence in the body may be learned from the fact, that the point of the finest needle cannot be thrust into any sensible part of the body without its withdrawal being followed by a drop of blood. This is the case not only in the external skin, but, could we try it, it would be observed also throughout the whole mass of the body, even in the bloodvessels themselves.*

34. Some of these capillaries are so very fine as to be unable, in a healthy state, to carry anything but the thin, colourless portion of the blood. Ex- amples of such are to be found in the tendons, lig- aments, nerves, and other parts which are white. The white parts of the eyes are striking instances. In these and other parts, even where they do con- vejf red blood, they are so fine that a powerful microscope can scarcely detect them. But when they are excited by disease to increased activity, they become enlarged by too much blood being forced into them, and those which should be white become red, and "inflammation" is the result. This mVy be seen in an inflamed or bloodshot eye, or in infcimmation of the skin, when the white ca- pillaries ire filled with red blood ; and it is pre- cisely the same condition of the capillaries which

* To provA that the Bones are supplied with capillary blood- vessels, Profe^or Mussey fed a pig on food mixed with madder, a vegetable vvlfch contains a great deal of red colouring matter. When the anini^l was killed, the bones were found throughout of a deep red c(^our, which could only have been conveyed to them by the circulating apparatus. One of the bones of that pig is m my cabir^t, presented by Professor M.

CIRCULATING APPARATUS.

37

constitutes inflammation of the lungs, stomach, brain, or any other internal part.

THE CAUSES OF THE BLOOd's PROGRESSION.

35. It is believed now by physiologists, that the power of the heart alone is not sufficient to propel the blood through the whole length of the arteries, but that this organ is aided by the vessels them- selves. Some suppose the arteries have a muscu- lar power, and others that their elasticity only is applied to assist in forvvarding the blood. Be that as it may, we will now merely advert to the me- chanical arrangement of the arteries and their branches, to show how well that is designed to help the blood along. We know when a fluid flows through a pipe of the same calibre through- out, that it meets with much resistance from the friction against the sides of the pipe. But if the pipe should increase in size gradually, from the end where the fluid enters to the other end, not only would the friction of the stream against the pipe be greatly diminished, and the fluid run along more easily, but a greater quantity could be sent through it.

^isr. 9. 36, Figure nine will ex-

emplify this fact. Let B represent a reservoir of water, and A a conical pipe discharging the wa- ter. A pipe of that shape will discharge more fluid than one of the same length whose diameter is the same throughout as at its com-

PlplfP

38

CIRCULATING APPARATUS.

mencement, "because the gradual expansion of the tube permits the stream from behind to force itself between the filaments,* and disperses them without producing that pressure on the sides of the tube which must take place where it is of uniform calibre."

37. Such is, in effect, precisely the arrangement of the arterial tubes, as explained in fig. 6.

" The celebrated John Hunter took great pains to prove that the artery had its diameter enlarged as it proceeded from the heart, and that the areas of the branches of an artery were greater than the diameter of the parent trunk.

Fig. 10. That is to say, the sec-

tion of the trunk at A is not so great as the two sections at B taken to- gether ; that the two sec- tions at B taken together are not so great as the four sections at C ; that the conjoined diameters,

' A therefore, of the branches

of an artery, are greater than the diameters of the artery itself. This fact has been sometimes ex- pressed by saying that the artery was a cone, with its apex in the heart."

It will be seen, there- fore, that although the cur- rent of blood is gradually

♦ ** Those who treat of hydraulics divide a column of water into ideal lesser columns, which they call fiiaments.'*^

CIRCULATING APPARATUS. 39

divided into a great number of smaller streams, it has more and more room as it advances, and, con- sequently, meets with less impediment to its prog- ress.

38. The manner in v/hich the blood gets through the veins is different from this. These vessels- have no power in themselves to push the blood along. They have no elasticity or contractility. To compensate in a great measure for the absence of those properties, they are placed in close con- tact with the muscles of the body, by whose con- tractions the veins are almost continually com- pressed at intervals, and as the valves prevent a reflux of the blood, it is thus forced towards the heart.

This force, conjoined with that of the arteries behind, is the principal means of propelling the blood through the veins.

39. There is yet a hydraulic principle discover- able in the construction of the veins which de- serves attention, and which, as in the case of the arterial circulation, may be explained by reference to its operation in inanimate tubes. It is shown in the mode or direction in which the smaller veins are connected with the larger, and in the manner in which they are assisted, by that direction, in discharging their contents towards the heart.

To understand more clearly the value of this arrangement, we must observe the modes of dis- tribution of the two classes of bloodvessels, and we shall see a strikins: difference between them in this respect. In the arteries the fluid flov/s from the trunk to the branch, and in a reverse direction in the veins ; and when we see a decided difference in

D 2

40

CIRCULATING APPARATITS.

the manner in which the trunks and branches of each are united, the mind is at once led to con- elude, that, as every fibre of the body is arranged in accordance with a previous design, there must have been a particular object in view in thus ar- ranging the bloodvessels, and we are urged to as- certain the cause or reason for this variation. Sir Charles Bell very ingeniously shows what the design in this case is.

40. The difference is this ; in the arteries the branch leaves the trunk with a slight divergence from the direction of the stream, while in the veint in which the current is in an opposite direction, the branch joins the trunk at nearly a right angle.

Fig. 11.

Number one in fig. 11 represents a sec- tion of an arterial trunk, with its bran- ches ; and number two the same of a venous trunk.

41. Let us now see whether these various distributions accord with the hy- draulic principles es- tablished in relation to currents through artificial pipes. " If a pipe be fixed into another contrary to the direction of the stream, the discharge into that lateral branch from the larger tube will not only be much smaller than we might estimate by the

CIRCULATING APPARATITS.

41

diameter of the tubes, it should be, but in certain circumstances it will discharge nothing at ail ; nay, the water will be drawn from the lesser tube into the greater.

Fig. 12.

" Bernouilli found that when a small tube B was inserted into the side of a horizontal conical tube A, in which the water was flowing towards the wider end C, not only did no water escape through the smaller tube, but water in a vessel at a consid- erable distance below was drawn through the les- ser tube into the greater."

Now by figure 10 we have seen that an artery and its branches discharge their contents on the principle of a conical tube, like A C, fig. 12 ; and the reader will at once perceive, that if an arterial branch were inserted into a trunk at or near a right angle, the fluid would not run from the latter into the former, but would be more likely to be drawn yrom the lateral branch.

42 CIRCULATING APPARATUS.

42. But this is precisely what is wa,nted in the venous circulation. The vein itself, being of ine- lastic material, has no power of its own, as has the artery, to assist the flow of the blood, and the ar- rangement of its branches just described compen- sates in a degree for that deficiency of its integral structure.

To render the wisdom of this arrano-ement more striking, let us suppose the reverse to have been the condition of the circulating vessels, viz., the arteries having their branches distributed as are those of the veins, and vice versa. The flow of blood through the arteries would then have been opposed by the hydraulic principle, as explained by fig. 12, and that through the veins deprived of the assistance now afibrded it by the present ar- rangement.

The result must necessarily have been a great retardation of the circulation through both sys- tems of vessels. While the diminished impetus of the blood in the arteries would have deprived the system of m.uch of its present energy and pow- er, the arrestation of it in the veins would have been a continual cause of congestions and inflam- mations.

43. Another beautiful illustration of the utility of this mode of distribution of the veins, and of the powerful aid it renders in advancing fluids, is given in the chapter on the digestive apparatus, in the description of the manner in which the contents of the thoracic duct find their way into the general circulation.

RESPIRATORY APPARATUS. 43

CHAPTER 11.

RESPIRATORY APPARATUS.

44. Having, in the foregoing pages, made the comparison between the circulation of water through a city and the circulation of blood through the body, to complete the analogy there is now to be described the manner in which the blood is pu« rified.

When this fluid leaves the left side of the heart to go to nourish the system, its colour is a fresh, bright vermilion ; but when it has reached the venous system its appearance is totally changed ; ?t is then a very dark purple, and almost black in colour. This difference constitutes the grand ap- parent distinction between arterial and venous blood. The former is alone fit for nutrition, be- cause it is pure and healthy, while the latter is loaded with impurities, and totally unfit to afford nourishment to the body.

45. When a bloodvessel is accidentally opened in the body, there are, therefore, two means of knowing whether it is an artery or a vein. From an artery, the blood will jet out in successive leaps, corresponding to the pulsations of the heart, and it will be of a bright red colour ; while the blood from a vein will ooze or run out in a slow, steady stream, and will be of a black colour.

This change in the colour and properties of the

44 RESPIRATORY APPARATUS.

blood is produced in its passage through the ca- pillary vessels. While in them the red blood yields up its healthy, nutritious particles, which are deposited in the various textures of the body, and the decayed portions of the various tissues are taken up and carried into the veins, to be taken to a place where they can be thrown out of the sys- tem ; or, in other words, where the black blood may be purified, revitalized, and restored to its life-sustaining condition by receiving fresh, healthy properties.

46. The organs devoted to the purpose of puri- fying the blood are the Lungs, which are two large bags situated in the chest, one on each side, and nearly filling up all those parts of that great cavity not occupied by the heart and large bloodvessels. It has been already stated, that the right side of the heart is devoted exclusively to sending the blood into the lungs (10). All the blood that flows into them (except a small quantity of arterial blood for the nourishment of their substance) is, of course, venous or black blood. The veins from the body empty their blood into the right side of the heart, and thence it goes to the lungs ; in them it becomes changed from black to a vermilion col- our, and then is transmitted to the lefl side of the heart, to be distributed through the body.

An intimate connexion, therefore, exists between the heart and the lungs.

47. The purification of the blood is effected by a chemical interchange of properties between it and the atmospheric air which enters the lungs during respiration. For this purpose the two are brought into very close communication with each

RESPIRATORY APPARATUS.

45

other, in the following manner. Each lung ig formed of an extremely fine and delicate mem- brane, in the form of a large sac, the cavity of which is made up of a countless number of very small cells, called air-cells, which are filled with air on inspiration. Each air-cell is accompanied by a capillary artery and vein, which are the final ramifications of the pulmonary artery and pul- monary vein transmitting the blood from and to the heart.

Pig. 13.

A view of the Trachea and its branches, with one lung at- tached. L, the larynx, at the upper end of T, the trachea. D the point of its division into its two main branched, called bron- chiae. L L the left lung. The two lines on its surface mark the fissures which separate it into three parts, called lobes. B B B B B are ramifications of the right bronchus. B 6 B 6 show their final terminations. Each little vessel opens into an air-celL

46 RESPIRATORY APPARATUS.

The air gets into the lungs through the wind- pipe T,* a tube situated in the throat, and running from the back of the mouth to the upper end of the breast-bone behind, at which point it divides into two branches, one of which goes to each lung. Each of these branches, when it reaches the lung, divides again, and these subdivide into minute ram- ifications, which finally terminate in the air-cells.

A pretty good idea of this arrangement may be had by supposing a large tree in full foliage, having two large main branches, and cut off at the earth and inverted. The trunk of the tree will represent the windpipe ; at a short distance from the end it divides into two principal branches ; these again divide into other branches ; and this division and subdivision is carried out so far that each branch finally terminates in little twigs ; and at the end of each twig is a leaf, the great numbers of which cause the tree to seem as if made up wholly of leaves. The leaves represent the air-cells. So it is with the lungs. As the windpipe and bron- chiae divide and minutely ramify until they termi. nate each in a little cell, it appears as if the lungs were totally composed of these air-cells.

48. Upon very close inspection of the organs themselves, it will be seen that around each air- cell circulates a number of fine capillary bloodves- sels, some bringing black blood and others car- rying bright red blood away. The blood circu- lates freely through these little vessels in contact with the membrane forming the cell, and in its passage through the vessel its colour is changed

♦ Technically called the TracfiM*

RESPIIIATORY APPARATUS*

47

by the chemical action of the air in the cell. The hlood does not come into immediate contact with the air, but they are separated only by a membrane so fine as to oppose no impediment to the necessa- ry chemical operation.

Fig. 14.

The heart, with the left lung in connexion. The upper halt of the lung is divested of its external membrane, to show its in- ternal structure. T the trachea. L B, its left branch, the ex- tremities of which terminate in the air-cells. P A, the pulmo-^ nary artery, P V, the pulmonary vein ; the former, by its capilla- ry terminations) taking the venous blood to the air-cells, and the latter, by its capillaries, taking the red blood /rom the air-cells. The lower half of the lung presents its natural appearance as seen in a healthy subject. 1 1, a magnified view of the air-cells. 2 2, capillary arteries going to the cells. 3 3, capillary veins running from them.

^ Before entering into an explanation of the inter*

48 RESPIRATORY APPARATUS.

esting chemical actions which take place in the lungs, we will examine the beautiful and ingenious mechanism by which the atmospheric air gets into the chest, and it will be seen that the ^physical part of the operation is arranged and conducted in per- fect accordance with well-known pneumatic laws. Our admiration is excited as much by its simpli- city as its perfect efficiency.

49. The human body contains three great cav- ities : first, that of the head ; second, that of the chest ; and, third, that of the abdomen. The first of these is filled with the brain and its apparatus ; the last, principally with the organs of digestion ; and the second, the chest, contains the heart and the organs of respiration. These three cavities are totally distinct from each other in their boun- daries, and although they have a very close vital connexion, they may, for the purpose of exhibiting their mechanism, be considered as entirely inde- pendent of each other.

The chest will comprise, therefore, all with which we have at present anything to do.

50. This great cagelike cavity is made up he- hind by the middle portion of the spinal column, at the sides and to'p by the ribs, m front by the breast- bone, and beneath by a broad muscle called the diaphragm. These constitute all the boundaries of the chest ; and it will be seen, by reference to •the figure below, how ingeniously the space is made as large as is compatible with its strength, and the graceful proportions of this part of the body (fig, 15).

S S represents the spine or posterior boundary of the chest. R R, the ribs, which are fastened by

RESPIRATORY APPARATUS,

49

Fig. 15.

C b the collar-bone, S b the shoulder-blade.

one end to the spine, and, making a large curve, go forward to be attached to B b, the breast-bone. The ribs do not touch the breast-bone, but are fas- tened to it by means of strips of cartilage, C C C|

50 RESPIRATORY APPARATUS.

which give to the chest much freedom of motion and great elasticity.

There are twelve ribs on each side, but they are all of different lengths, the shortest being at the top, and having the smallest curves ; as they de- scend, they increase in length till the seventh, which is the lonorest. From the seventh to the twelfth they decrease in length, the cartilages be- coming longer in proportion, except the last two, which have no cartilage and no attachment other than at the spine.

The ribs are attached to the spine by a joint which is slightly moveable.

By examining the preceding figure, it will be ob- served that the ribs do not lie horizontally, but their front ends are much lower than their hinder ends ; they run downward as they run forward. This is an important point in the mechanism of respiration, and must be particularly recollected.

51. The next part of the apparatus to be de- scribed is the Diaphragm, This is a broad sheet, composed of muscle and tendon, of a circular form, and completes, when in its natural position, the lower boundary or floor of the chest (fig. 16).

The circumference of this circular muscle is attached to the inside of the front ends of the ribs, to the lower end of the breast-bone, and to the spine behincl. It does not lie Jiat, but its centre is pushed high up into the chest, so as to form a great con- vexity in that cavity, and a concave surface on the under side. It forms a complete separation be- tween the chest and all the parts below it, except where it is perforated by the large bloodvessels and

KESPIKATORY APPARATUS*

51

Tip;. 16.

The front half of the ribs being cut away, the interior of the chest is exposed. C c C c, the cavity of the chest, empty. D D D D, the diaphragm, rising high in the centre, and descending Very low at the sides and behind. The white space at its upper part is its tendinous portion. A A, the abdomen.

nerves, which pass up and down, and by the oesoph- agus or food-pipe, which goes through it into the I stomach.

I 52. To complete the walls of the chest, there ] remains now only to be shown the filling up of the f spaces between the ribs ; and this is effected in such a manner as to add very considerably to the respiratory power of these organs. All those spaces are occupied by strong muscular fibres, whose arrangement and uses can be best explained by a figure (fig. 17).

52

RESPmATORY APPARATUS.

Fig. 17.

R R will represent sections of two ribs, and M will show the direction of the two sets of muscular fibres which run from one to the other.

There are two layers of muscles placed between the ribs, whose fibres cross each other, as in the cut. These muscles fill up entirely all the spaces between the ribs, and their object is to bring the ribs closer to each other by their contractions, an object much more readily gained by this arrange- ment of the fibres than if they went directly from one rib to the other in the direction of the dotted lines L.

The reason is obvious ; for if they can only con- tract one third of their length, which is believed to be the maximum extent with any muscle, the per- pendicular fibres would be able to bring the ribs only that much nearer together ; whereas the ohiique fibres, with the same degree of contraction, by acting together, will nearly close the interve- ning space. This afibrds another striking proof of the ingenuity of the designer of this curious mechanism.

53. Most people who have not given nrrach thought to the subject, would answer, if they were asked to explain how the air gets in the lungs, that they supposed the air rushes in at the mouth and

RESPIRATORY APPARATUS. 53

pushes the ribs out, and so the lungs become filled. And then if they are told that if the mouth were held wide open a whole day, and no exertion made, no air would go in, they would probably be unable to tell anything about it. They might with as much truth say, if a pair of bellows were lying un- touched on a table, the air would rush in through the nozzle and push the boards asunder.

But every one knows, that if the boards of the bellows are pulled apart, then, in obedience to a well-known law of pneumatics, the air goes in through the valve and nozzle, and occupies all the space between them. And when the boards are pressed together again, the air is forced out through the proper opening.

Such is precisely the manner in which the air is made to enter the chest. This cavity is first greatly enlarged, by which a vacuum is produced, which vacuum is instantly filled with air entering through the only opening there is, viz., the mouth, which leads to the windpipe. The air is thus said to be inhaled ; and when the chest contracts its dimensions, the air is forced out at the mouth, and is exhaled. The alternate expansion and con- traction of the chest are not merely passive opera- tions, but are both produced by the action of a powerful set of muscles, called respiratory muscles^ of which the diaphragm and the muscles between the ribs form an important part.

54. The enlargement of the chest is made in three directions. First, the diameter from side to side is increased ; second, the diameter from the spine to the breast-bone is also elongated ; and,

54 RESPIRATORY APPARATUS.

lastly, the length from top to bottom is very much extended.

The first enlargement is produced simply by el- evating the sides of the ribs. The spine is the fixed point upon which all the motions of the ribs are made ; and by referring to fig, 15, it will be perceived, that if a rib is raised and turned a little on its joint at the spine, in consequence of the pe- culiar direction of the rib before noticed, the mid- dle portion of it will be thrown farther from the centre of the chest, and, consequently, the two sides of the chest will be farther separated from each other.

Secondly, by the same elevation of the ribs, their front ends are brought more on a line with their other ends ; and to permit this motion, the breast- bone must be raised and pushed a little forward. Any one may be convinced of the first of these motions by placing one hand upon each side, and feeling the elevation and protrusion of the ribs ; and of the second, by laying his hand upon his own breast, or looking at another's. The motion of the bone may be distinctly seen, but more especially after severe exercise, as running, when the breath, ing is " hard." These motions are commonly called the " heavings of the chest."

55. The enlargement of the chest from top to bottom (the third) is produced solely by the dia« phragm, without any active aid from the ribs. This organ has been described (51) as situated in such a manner that, when in a state of relaxation, it forms a convexity within the chest, and is very concave or hollow underneath. It is, in fact, shaped like a dome, or an upper segment of a hollow

RESPIRATORY APPARATUS.

55

globe. When the fibres of the diaphragm con- tract, its centre is brought down nearer to a line Vvith its circumference ; in a word, it is partial- ly flattened. This organ being the floor of the chest, of course, by being thus lowered, it leaves more room above it ; and it adds very materially to the size of the chest.

Fig. 18.

Sections of the chest, diaphragm, and abdomen. These cuts represent, in section, the different positions of the diaphragm in its conditions of re- laxation and contraction, and also the different cor- responding conditions of the abdomen and chest. In No. 1, D, the diaphragm is greatly contracted,

56 RESPIRATORY APPARATUS.

whereby the chest is enlarged, and the abdomen, M M, is protruded. In No. 2, D D, the diaphragm is relaxed, and the chest and abdomen correspond- ingly altered in size and position.

56. Now all the motions above briefly described take place simultaneously. The first two are pro- duced by the action of strong muscles placed out- side the chest, aided by those between the ribs ; and these and the diaphragm all acting together, they have a great effect in increasing the capacity of the cavity within.

This great enlargement produces, as has been said, a vacuum within, which is supplied as soon as made, by the air rushing in at the mouth.

57. But it must be recollected that the air which enters the chest does not get into the cavity itself, but into the air-bags or lungs within the chest. These have no power of themselves to expand, be- ing made simply of fine membrane, without a par- ticle of contractility like muscular fibre ; but, as the chest enlarges, the air rushes into them, and swells them out so as to fill up the cavity.* If an open- ing should be made in the lung to communicate with the cavity of the chest, then some of the air which enters the lung would get into the chest, and the lung would not so fully expand. Very un- pleasant and dangerous symptoms would be the result of such an accident.

58. To explain more clearly the mode in which air gets into the lung, a little model is frequently

♦ By placing one's ear against the chest of a healthy person, the noise made by the air passing through the kings may be dis- tinctly heard in a quiet room. The sound of the action of the heart may be perceived also, if the ear is placed over that organ.

RESPIRATORY APPARATUS.

57

exhibited, of which the figure in the margin is a representation.

C C is a bell-shaped glass to /ig. 19. represent the chest. In the

mouth of the glass is inserted very tightly a cork, T, rep- resenting the trachea, having a hole lengthwise through it. To the lower end of the cork, before it is put in its place, is tied a small bladder, L, to rep- resent a lung. The lower end of the bell is closed by a piece of sheet gum elastic, D, which is closely pasted around the edge ►so as to be perfectly air tight. This answers for the dia- phragm. It is clear that no communication exists between the cavity of the bell and the external air, except through the hole in the cork, and any air entering through that hole can only go into the bladder. It is evident, also, that when the diaphragm is pushed up into the cav- ity of the glass, as at D, the bladder will be flaccid and void of air ; but when the diaphragm is pulled down in the situation of the dotted lines, a par- tial vacuum in the glass will be the consequence, which can only be supplied by air through the cork, which will expand the bladder to its full ex- tent, shown by the dotted circle ; and when the di- aphragm is pushed up again, the air will be forced out from the bladder. i

To complete the model, a hollow paper doll's head may be placed on the cork, having the

58 HESPIRATORY APPARATt^Sa

mouth communicating with the bladder. By vary- ing the size of the mouth, different sounds, as of breathing, whistling, &c., may be produced, and a candle may be blown out by it.

The diaphragm in the living body does not de- scend so low as in the figure, for much motion is re- quired from it in the latter to compensate for the ab- sence of expansion in the other parts. In the body, its centre does not descend to a level with its cir- cumference. With this instrument, the model of only one lung can be shown, but it gives us the ad- vantage of seeing its action.

59. It has been stated that the object of the lunffs is the purification of the blood ; but this is not the only result of their operations. It is doubtless owing to the chemical action continually going on in them, that the body is indebted for the constant maintenance of its uniform, elevated temperature. One of the most curious results of animal action is^ that the body, under the greatest variety of exter- nal circumstances, is always found to have a tem- perature of 98° of Fahrenheit's thermometer. Whether we inquire of the inhabitants of India, living under the scorching rays of a tropical sun, or of the frozen regions of Labrador or Iceland, where they are surrounded with eternal snows, we shall find the temperature of the body to be inva- riably the same. The lungs are the furnace where the necessary caloric is developed, and from which it is distributed through the system ; but the principal regulator of the temperature is the skin, an organ to be described hereafter.

60. Many different theories have been suggested by physiologists to account for the change in the

HESPIRATORY APPARATTTS. 59

colour of the blood, and for the evolution of ca- loric ; but we shall only attempt to explain the one which is the most probable.

Chemistry teaches us that atmospheric air is composed of two distinct elementary gases, v/hose properties are very different. They are called nitrogen and oxygen. The former constitutes about four fifths of the air, and the latter one fifth. Nitrogen gas, when pure, possesses no active prop- erties ; it will not support either combustion or animal life, nor will it destroy either by any pe^ culiar power of its own. On the contrary, pure oxygen has many active and powerful properties. Bodies not commonly inflammable will burn in it with great rapidity and brilliancy, and animals live in it with increased activity ; but they cannot live so long in it as in the open air. They die sooner^ as they seem to live faster.

Oxygen is, in fact, the vital principle of the at- mosphere, and without it, combustion and life would both be extinguished. It is supposed by some that the nitrogen is combined with it principally to di^ lute it, to render it less active, but not to destroy any of its qualities.

61. Oxygen is the principal material which, when received into the lungs, causes the change in the colour and properties of the blood, and deveL opes the requisite caloric. The venous blood owes its dark colour chiefly to the presence of carbon, another simple substance commonly known to us as charcoal, which is chiefly pure carbon. Ani- mal bodies contain a good deal of carbon in a subtile form ; and it is well known that oxygen has a powerful affinity for it, and will generally unite

P

60

RESPIRATORY APPARATUS.

with it to the exclusion of other substances. The product of such a union is another substance call- ed carbonic acid gas. When charcoal burns in the open air, this gas is produced ; and being a very deleterious and poisonous substance, fatal conse- quences often ensue to those who breathe it. It is easily proved that this gas is formed in animal bodies during the process of respiration ; and as it 2an only be formed by the combination of oxygen ind carbon, and as we can show that all the oxy- gen which is inhaled does not return as oxygen, 3ut in the form of carbonic acid, the fair inference is, that it has taken carbon from the blood. We inhale nitrogen and oxygen in the form of atmo- spheric air, we exhale nitrogen and carbonic acid gas. The oxygen, therefore, must have quitted the nitrogen and combined with the carbon.

To prove that carbonic acid is contained in the exhaled breath, it is only necessary to blow it a few minutes through a small tube immersed in clear

ig. 20.

RESPIRATORY APPARATUS. 61

lime water contained in a vial. The gas has a strong affinity for lime ; and, when passed through that liquid, it unites with the lime, forming a light powder, which is insoluble, and gives to the fluid a cloudy appearance (fig. 20).

62. Besides this gas, there is thrown off from the lungs a large quantity of watery vapour, amounting, as is estimated by some, to twenty ounces in twenty four hours. The fact that a large quantity is expired with every breath, may be proved by breathing upon a cold polished sur- face, as of glass or metal. The vapour condenses, and rapidly accumulates in drops.

63. The dark blood being in this manner de- prived of its carbon, it must be apparent to any one who thinks a moment upon the subject, how important it is to a healthful action of the lungs to have a free supply of fresh air. Almost every- body can testify, from their own experience, to the disagreeable effects produced by confinement for a length of time in a close room, especially when a number of individuals are collected therein. Each person respires about twenty times a minute, and takes in at every breath about forty cubic inches of air (rather more than a pint), the oxygen of which is not only nearly all used up, but forms part of a substance as positively injurious to health, as are the fumes of burning charcoal. When, therefore, a number of persons for a long time breathe the same atmosphere, without any ventila- tion or renewal of it, they rapidly exhaust the air of its healthy properties, and subject themselves to great dangers. The reason is this : No pure, fresh oxygen being admitted to the lungs, the dark blood

62 RESPIRATORY APPARATUS.

cannot part with its carbon, because this gas is the only means by which it can be taken away. The blood, therefore, does not become revitalized ; it has to go back to the heart from the lungs in its impure state, and it is sent through the body total- ly unfit to give it proper nourishment. The whole system partakes of the injury ; the brain and spinal marrow, which are the centres of the nervous power, become unable to discharge their high func- tions properly ; the action of the heart and lungs becomes thus still farther impaired, and so, directly and indirectly, the entire body becomes rapidly surcharged with vitiated blood, and, unless speedily relieved by the admission of fresh air to the lungs, fatal results must ensue. Persons who have been sitting several hours in a crowded church in cold weather, when the doors and windows are all closed ; even children confined for five or six hours in a close schoolroom of small dimensions, without ventilation, as is the barbarous practice in too many places in city and country, exhibit the de- pressing effects of imperfectly decarbonized blood in their drowsiness and the general torpor of the body. They perceive the striking difference be- tween good and bad air — between that which con- tains plenty of free oxygen, and that which con- tains but little — when they emerge from their con- finement and inhale the first draught from without. The spirits immediately revive, and new strength seems imparted to the body.*

* It was once remarked, that in Scotland they formerly had long sermons against " the sin of sleeping in church," but by increased knowledge it had been found out that a perfect ventilation of their churches did more to keep people awake than all the sermons illustrative of the sin of "church sleeping.'

RESPIRATORY APPARATUS. 63

64. Among the numerous instances of danger and suffering from confinement in an atmosphere vitiated by passing repeatedly through the lungs, the occurrence at the " Black Hole" of Calcutta is one of the most memorable and melancholy. In 1756 the city was reduced by Surajah Dowlah, and 146 English prisoners were forced into a dun- geon about eighteen feet square. The only open- ing to the air, except the door, was by two win- dows on the west side, strongly barred with iron. In a few minutes a profuse perspiration burst out upon every one ; a raging thirst ensued. In less than an hour after their confinement, their thirst was intolerable and respiration difficult. Many soon became outrageous, and insulted the guards to induce them to fire in upon them. " Water, water," was the general cry ; but, when brought, it only served to aggravate their distress. The con- fusion became general, and amid horrid cries and ravings for water, some were trampled to death. In less than three hours, most of the gentlemen were dead ; and in half an hour more, most of the living were in an outrageous delirium. They found that water heightened their uneasiness, and " air, air," was the general cry. All the opprobri- ous names that the viceroy and his officers could be loaded with, were repeated, to provoke the guard to fire upon them. Every man had eager hopes of meeting the first shot. Having been shut up at about eight o'clock in the evening, the door was opened at six the next morning, when only twenty- three, the poor remains of 146 souls, came out alive, but most of them in a high putrid fever.

65. In connexion with this subject, there is an- other which deserves some attention, as it affects

F 2

64 RESPIRATORY APPARATUS.

the health and lives of many individuals in as great a degree as this.

The lungs have been described as two large sacks of extremely fine texture, filling up by their size every 'particle of the space hetween the ribs not occupied by the heart, the large bloodvessels, and the membranes covering them. They can re- ceive no more into them than is sufhcient to sup- ply the increased capacity produced by the en- largement of the chest. The respiratory muscles enlarge the chest to a certain extent, and a quan- tity of air just sufficient to fill the chest, but no more, enters the lungs. All that we can possibly get is necessary to purify the blood thoroughly ; and if, by any cause, the requisite quantity of oxygen is pre- vented from reaching the lungs, the system feels very soon the effects. Those who live in the crowded, smoky, and dusty atmosphere of a popu- lous city, experience this. So much of the air is unfitted for respiration, that there is not a propor- tionate quantity of oxygen taken in at each inspi- ration, and very frequently through the day, un- consciously, in general, to the individual, nature in- stinctively makes an effort to compensate for the deficiency by producing one or more deep and co- pious inspirations. How often is heard from the citizen, when he first enters the pure atmosphere of the country, the exclamation, '' How much easier it is to breathe !" Less labour is there really re- quired from the respiratory apparatus, because the dark blood is more rapidly and effectually decar- bonized.

6G. If, then, pure air is so essential to the healthy operations of the lungs, what must we think will be the effect of preventing their expansion and of to^

RESPIRATOR y- APPARATUS. G5

tally excluding from them a large proportion ot ihe air which they might have. We have shown the chest to be a flexible elastic cage ; a considerable portion of its walls is made of elastic cartilage, which v/ill readily yield to pressure {^g, 15). The object of these cartilages is principally to assist in bringing the chest to its former size, to produce expiration after it has been enlarged in inspiration. Their flexibility may be proved by placing a hand on each side and pressing them together ; the sides can thus be made to yield several inches. The most cursory observer must therefore perceive, that if a bandage is tightly drawn around the chest, and continued there for hours, not only will the chest be prevented from fully expanding by the con- finement of the diaphragm as well as the ribs, and a great quantity of air be shut out from the lungs, by which the venous blood will be unable to give off all its carbon and other impurities, but the right side of the heart must labour harder to propel the blood through the constricted lungs, and the left side also to keep in motion a fluid less suited to its iction. The delicate valves have an unnatural luty to perform ; and, finally, apart from the dis- ressing palpitations almost universally experienced ;y those who yield to such habits, enlargements )f the heart, thickness of the valves, consumption, md a long train of painful disorders ensue to im- jitter and shorten their days. Nature, or, rather, the wants of the whole system, endeavour to com- pensate for the artificial privation by increasing the exertions of the respiratory organs ; the chest is compelled to a great freq^uency of action, and

66 EESPIRATORY APPAKATTJ&.

hence inflammation of the lungs is often anothe. result.

67. This is not all. We have already alluded to the effect produced by undecarbonized blood upon the brain, the seat of the intellectual faculties, clouding and obscuring its operations. Several other evil effects are felt by this organ, but they must be considered in more appropriate places.

Tt is bad enough to be obliged to breathe a vitiated atmosphere, but to exclude the delicate lungs from the use of even that, to deprive the impure blood of a part of that restoring power, imperfect as it is, and to drive the already overburdened heart to still greater efforts, is a practice baneful to the health, destructive to the intellect, subversive of the mor- als— it is suicidaL

68. To exhibit more distinctly the effect upon the conformation of the chest, from the barbarous practice of " tight lacing," the accompanying fig- ures are subjoined. There is no exaggeration in these outlines. Such melancholy specimens are daily to be met with, both living and dead.

No. 1, fig. 21, is an outline of the famous statue of the Venus de Medici, and may be considered as the beau ideal of a fine female figure.

No. 1, fig. 22, is part of the skeleton of a simi- lar figure, with the bones in their natural position.

No. 2, fig, 21, is an outline of a figure of a mod- em " boarding-school miss" after it has been per- manently remodelled by stays.

No. 2, fig. 22, is the skeleton belonging to such a figure.

What individual, laying the least claim to a re- fined and correct taste, can hesitate for a moment

RESPIRATORY APPARATUS.

67

3

o

C3

o o

a

3

c

o

o •-«

w

5*

to

w

I

o

'a

ZD

at

s g

o o

RESPIRATORY APPARATUS. 69

to give the most decided preference to the former of these as the " finest figure." It is true, it does not accord with the views of the fashionable world ; but if that class of people must torture and twist some part of their bodies, far better would it be for them to apply the screws to the feet, as do the Chinese, than to the chest. Such a " fashion" would be no more absurd, less uncomfortable to the individual, and less dangerous to life.

69. The aqueous vapour which is exhaled in

such large quantities (62) from the lungs, is be- H

lieved to be also produced by the agency of oxy- gen. One of the impurities of venous blood is sup- posed to be another gas, called hydrogen, which is well known to have a strong attraction for oxygen, by which water is formed ; that fluid being com- posed solely of these two gases.

70. To these two chemical operations, viz., the I formation of carbonic acid and of water, are sup- I posed to be attributable the evolution of the heat », necessary for the system. Increased specific ca- I loric is an invariable eflTect of these combinations fiout of the body, as every chemist knows, and there I is no good reason why it should not be so in the I lungs. It is true that the lungs are not any warm- er than the most distant part of the body, as might DC supposed would be the case ; but it is to be rec-

3lollected that the circulation of the blood through {,;he chest is three times more rapid than the res- biration, i. e., the heart pulsates three times, and jijometimes more, to one expansion and contrac- ;ion of the chest. The caloric which is generated ;here is therefore carried away as fast as formed,

70 RESPIRATORY APPARATTTS.

and distributed by the blood equally through the entire system.*

* This is the rationale given to the process of calorification in the animal body by many distinguished physiologists ; but there is another view of the mode and situation in which it is carried on, which is in many respects equally plausible.

Carbon is supposed to be set free in the blood principally by the conversion of albumen into jelly, a process which takes place all through the body, but more particularly in the skin, through the agency of the capillary arteries.

Jelly is well known to form a large constituent of the skin of all animals. The oxygen taken in at the lungs is supposed to enter into the blood in a state of loose combination, and to be carried through the system, uniting with the disengaged carbon in the capillary circulation, and the carbonic acid to be conveyed by the veins back to the lungs to be exhaled. The combustion of carbon and oxygen is thus made to impart its caloric imme- diately at the spot where it is wanted, and the main fire that supports the temperature of the body is placed where it is most needed, at the external surface.

VOCAL APPARATUS. 71

CHAPTER IIL

VOCAL APPARATUS.

71. CoNNJ:oTED with and depending upon the function of respiration, is another highly curious and interesting mechanism now to be described. It is an instrument of very deUcate and somewhat com- plex construction, and is adapted to several uses, or, rather, to a variety of modifications of the same office. In infancy, it is an instrument by which the child can make known to the parents its wants ; by which alone it is able to apprize them of its suffering when in pain, and to warn them to bring relief. In later hfe, it is an organ by whose agen- cy individuals are enabled to make known to oth- ers their thoughts and feelings, with most unerring precision ; it is, in fact, the great outlet of the workings of the mind. It is, finally, an apparatus capable of producing the most exquisite music. It may rival the flute in softness of tone ; its shrill- ness is not surpassed by the "ear-piercing fife ;*" Its mildness may equal the clarion's ; and in mel- lowness of note or soul-stirring energy of sound, the trumpet does not approach it.

72. This instrument is composed of several parts, which, when all are considered together, are called the Organs of Voice, One part of the apparatus operates as a stringed in^rument, like the Eolian liarp. The latter is made simple by stretching a

72 VOCAL APPAEATtTSr

fine thread of silk across a board, about an inch above it, and placing it in the window-frame, with the sash brought down so as nearly to touch the string. As the breeze passes through the open space, it strikes the string and causes it to vibrate, by which a variety of niusieal sounds are produced. Another part of the vocal apparatus acts on the same principle as a valvular wind instrument, such as the valve trumpet or the common flute ; or, as it has a pair of bellows (the chest) to force air through the instrument, it may be said lo act like a church organ.

73. The windpipe, which has been described as the tube through which the air passes to the lungs, lies in the forepart of the throat. It is formed chiefly of cartilage, which, at the lower two thirds of its ext^:it, is seen in the form of rings (imperfect behind), which may be felt in the lower part of the throat. These rings, being elastic like all carti- lage, serve the very necessary purpose of keeping the tube always open, that no in>pedimcnt may ex- ist to tlie passage of the air. They will yield to pressure, but will instantly recover their natural form when the pressure is removed ; at the same time, the fl^exibility of the tube will aeeommodate it to any position of the neck.

This tube is surmounted by a triangular box, also formed of cartilage, the greater prominence of which, in the man, produces the striking difference in the shape of the neck of the two sexes. This box is called the Larynx* Tlxe prominence in the neek formed by the larynx is commonly known- by the name of Adam's Apple ; from an old story that, when Adam swallowed the forbidden fruit, it

VOCAL APPARATUS.

73

stuck in his throat, and is thus transmitted to hia posterity as a memorial of his falL

Fig. 23.

T represents the upper portion of the trachea or windpipe, formed of im- perfect rings. The open space behind is filled up by a muscular membrane. _ L is the larynx, forming the upper end of the windpipe. H H are the two ends of a bone, which is shaped like the letter U, with the ends turned up. This bone is placed at the upper edge of the larynx, and serves to keep it stretched constant- ly open, and also for the attachment of several mus- cles*

The upper opening of the larynx is a simple slit or chink about three fourths of an inch long and one fourth wide. At the low- er part of this chink are found stretched across two fine ligaments, which are directly in the current of air as it goes through the tube either way. These ligaments, by appropriate little muscles, may be relaxed or made tense, and being thrown into very rapid vibrations when the air rushes through them, produce every variety of sound.

74. The top of the trachea opens above into the

74 VOCAL APPARATUS.

back part of the mouth, just in front of the opeir- ing of the tube leading to the stomach. All the food and drink, therefore, which we swal- low, before it gets to the stomach tube, must pass directly over the top of the larynx. As even a small particle of food produces very distressing symptoms when it happens to get into the w-rong passage, the larynx is most beautifully provided with a means of protection. Directly over the chink just described is placed a little valve, mark- ed V in fig. 23, which shuts down over it the in- stant anything touches it, and closes the opening completely, so that the food passes by it into its proper place. Sometimes, when a person is eating very fast and talking at the same time, small par- ticles of food will get into the windpipe ; this tube being lined inside by an exceedingly sensitive membrane, pain and suffocating symptoms are pro- duced, the chest is thrown into violent spasmodic action called coughing, and generally the offend- ing substance is thus thrown violently out, and the distress ceases. Sometimes it happens that a small substance, as a grain of wheat, a shot, a fruit-stone, or a particle of food, gets very far down into the windpipe, so that the individual is unable to cough it up. A train of terrible symptoms then generally ensues, terminating sooner or later in a painful death. Man}' chilch'en have lost their lives in that way, and neither infants nor nged should ever be in the practice of keeping small articles of unyielding substances in their mouth, for fear of such an accident.

The other part of the vocal apparatus is the mouth, comprising the cheeks, tongue, teeth, and lips.

t)F THE BLOOD. 7§

The tongue and lips particularly act, as occasion requires, like valves or stoppers, changing the size and position of the orifices through which the air passes out, giving rise to most of the varieties of intonation and cadence in speaking.

'i

CHAPTER IV.

OF THE BLOOD,

75. The investigation of the circulating appara*. tus which we hav« just completed, leads us very naturally to inquire more particularly into the na*. ture of the fluid which it is the province of the ves* sels to convey through the system. Of all the liquid materials known to man, tlie Blood of ani^ mals is not the least, if it is not the most, remark- able. Of a peculiar colour, distinguishing it from all other fluids, it possesses a variety and multu plicilp of properties altogether unrivalled. There are many fluids which exhibit more strikingly eru ergetic qualities, such as the corrosive mineral and Vegetable acids, &c. -^ but we shall perceive that the blood, when acting its peculiar part in the ani- mal economy, is capable of distilling, as it were^ from itself, a. solvent (the gastric juice) of more va- rious and extensive action than any known acid.

76. The blood, moreover, is supposed to hold in solution, while in vital communication with the body, all the materials which are necessary to pro-

G2

16 OF THE BLOaD->,

duce every tissue in the animal structure. The means by whicli it does this, or, rather, the laws through whose influence, whether chemical, me- chanical^ electrical, or other, this is effected, have hitherto entirely eluded the researches of the most expert experimenters and profound reasoners. That an almost innumerable range of materials unite to make up this singular fluid, is clearly de- monstrated by its giving them forth continually and depositing them in their proper places ; and yet the chemist can detect in^it none other than well-knov/n chemical substances. While it is known, also, that from the blood are developed matters the most dis- cordant and opposite in character, such as water and oil ; acids highly corrosive, and alkalies pun- gent ; the inflammable phosphorus, and sulphur, and the incombustible soda or lime ; the hard en- amel, the tough tendon, and the delicate and tender nerve ; a great variety in colour, as the black pig- ment of the eye, the white membrane, the red mus^ cle, the yellaw hair, and the iris as variegated as the rainbow ; the dense bone, the semi-opaque nail, and the coniea, as transparent as the purest glass ; the bitter gall, and the insipid saliva ; while all these, and many other equally diversified proper- ties, are known to be continually separated from the blood, this fluid itself presents, in its ordinary pure form, scarcely a trace of many of these prop- erties. It only appears to us as a homogeneous fluid, of a uniform colour, slightly saline taste, in- nocuous to the touch, but when analyzed it is found to be complex in its chemical composition.

To facihtate the study of this unique substance, we may arrange its properties under three head&

OF THE BLOOD. 77

or divisions, viz., Physical, Chemical, and VitaL Though in some points we may find the properties under these heads to assimilate, yet the distinc- tions, in the main, will be sufficiently obvious to justify such a classification.

PHYSICAL PROPERTIES OF THE BLOOD.

77. a. Colour. — In man and the higher order of animals, the blood, when first drawn from the cir- culating vessels, is of a red colour (except when distinguished as arterial and venous blood, 44, 45), having rather a soft vermilion tint. This col- our is uniformly the same in these animals- in a healthy condition, and is not subject to much change even by disease. When the respiratory function is disturbed, either from an inability of the chest to admit air, or from the admission of im- pure air, the decarbonization of the venous blood is imperfect, and the blood found in the arteries will partake more or less of the 'purple hue of that of the veins. But the characteristic redness of healthy arterial blood is always more or less dis- tinguishable.

In some of the lower orders of animals, the blood is of a very different appearance ; it is in them called white Mood, being entirely devoid of redness, and almost colourless. With white-blooded ani- mals, the muscles are also white, as with fishes, frogs, reptiles, &c.

b. Consistence. — Immediately upon being taken from the body, as is well known, the blood is seen to be a perfect fluid, nearly or quite as thin as wa- ter. This condition is necessary to it in the blood- vessels, that it may circulate through the intricate

T8 OF THE BLOOD.

mazes of the inconceivably minute capillaries, as well as through the larger arteries and veins, with the least possible obstruction. In the living, healthy body, there is very little more adhesion be- tween the different particles of the blood in circu- lation than there is between the particles of water flowing through the conduit pipes of a city ; and as long as the active motion of the blood is kept up, so long will it maintain its complete fluid form.

But when allowed to remain at rest for a short time, particularly out of the body, a remarkable spontaneous change occurs in the form of the blood. One part of it loses its liquid consistence, and- falls to the bottom of the containing vessel, while the remainder retains its fluidity, but under- goes other important changes. This phenomenon is denominated coagulation. The process, as ob* served under ordinary circumstances, in an open vessel, commences with an apparently uniform thickening of the whole, and a gradual separation into two distinct parts, the one being a viscid, heavy mass of a red colour, and the other a thin, watery fluid, colourless, or, perhaps, slightly yel- low. The former is called the crassamenium or clot, and the latter the seru?n.

The scrum is the fluid which is drawn from the body by the action of a blister.

When submitted to the action of heat or alco* hoi, it also coagulates and divides into two parts. One a dense matter, which resembles the white of an egg boiled hard ; it is essentially the same sub- stance, and hence is called albumen. The other part of the scrum is a limpid fluid, denominated the serosUy,

The average time required for the completion of

OF THE BLOOD. 79

the coagulation of the blood is about seven min- utes, in the open air.

The most accurate investigations have shown the average amount of the crassamentum to be about one third the weight of the serum.

If the blood, when flowing from an open vein, is received into a bottle, and violent agitation is given to it, the formation of the clot may be altogether prevented, especially if the temperature of the blood is kept at its natural elevation.

On this account as well as others, we may see the necessit}^ of maintaining the activity of the circulation by frequent exercise, and of avoiding such a course of living as will tend to thicken, and thus retard, the motion of the blood. The Asi- atic Cholera, when it appeared in this country a few years since, was characterized by a remarka- ble torpidity of the circulation and coagulated state of the blood. The serum was usually discharged in enormous quantities from the skin, kidneys, and bowels, leaving behind only the crassamentum, which could not pass freely through the vessels, and the circulation was thus greatly impeded.

Rest, therefore, seems necessary for the success of the process of coagulation. In the living body, as well as without, the blood will undergo this change, even without any reduction of its temper- ature, if all motion between its particles is sus- pended. This occurs in the surgical disease call- ed Aneurism, which is an enlargement of an artery, forming a hollow tumour, filled with blood, by far the largest portion of which does not circulate freely. It happens, also, when a bloodvessel be- comes ruptured near the surface of the body, let-

80 OF THE BLOOD.

ting out a small quantity of its contents, which, being unable to escape entirely, coagulates around the opening in the vessel, and forms a kind of plug, which checks any farther bleeding.

When the clot is minutely examined after being removed from the serum, it appears under the form of a soft solid, sufficiently firm to bear cutting with a knife. It retains all the red colouring matter of the blood, and this, by repeated ablution in water, may be entirely separated from it, leaving the clor of a clear white, showing the union to be merely mechanical, and not dependant upon any chemical affinity. The white mass remaining is called fibrin, and very closely resembles the pure muscu- lar fibre.

Fig. 25,

Fibrin of the blood.

The cause of the coagulation of the blood has never been satisfactorily explained, and the laws which regulate it are not yet known to us. It is a phenomenon to which we are acquainted with nothing exactly similar; but especially are we un- able to understand the reason why many causes of

OF THE BLOOJy^ 81

sudden death entirely prevent the process: as lightning and electricity, a blow upon the stomach or chest, an injury of the brain, bites of poisonous animals, and violent mental emotions. These, when they produce the sudden extinction of life, prevent the usual coagulation of the blood.

It is upon the fibrin that the property which the blood possesses of repairing injuries of the solids of the body principally depends, a property which affords one of the most interesting examples of the resources of the animal economy. When an in- cision or laceration of the body happens, the blood issues from the divided vessels, fills up the wound, and then coagulates, unless a very large vessel should be wounded, and the blood flow too rapidly and escape. The clot remains, while the serum evaporates. Organization then takes place in the fibrin ; that is, new bloodvessels are formed in it, connected with the adjacent old ones ; new nerves also are produced through it, and it soon becomes a living mass. Rest and quiet are all that nature requires to complete this process ; the simplest dressing to a common wound is, therefore, all that is required. In former times, a common practice was to apply a sympathetic powder to the instru- ment which produced the wound, and merely bind the latter up. The cure was then attributed to the action of the powder on the instrument, and that superstitious notion was believed in a long time, and until it was discovered that the wound would do just as well without dressing the instrument* The true secret consisted in keeping the wound quiet.

c« Temperature. — The circumstance of th0

82 OF THE BLOOD.

maintenance of the temperature of the blood at a uniform standard, 98°, under the greatest changes of cHmate and the most varying conditions of the external world, is among the most curious of the phenomena of this wonderful fluid. The cause of its elevated warmth, and the reasons of its unifor- mity, are noticed at more length in the chapters on respiration and the skin. The temperature of white-blooded animals is much below that of the red-blooded ; they are hence called " cold-blooded" animals.

d. Quantity. — The amount of blood in different individuals varies considerably ; and it is a very difficult matter to arrive at a satisfactory conclu- sion of the average quantity, principally for the reason that there is no mode by which the actual amount in any one person can be ascertained. Taking all circumstances into consideration, it is believed that the blood constitutes about one fifth of the whole weight of the body. A man of 150 pounds, therefore, would have about thirty pounds of blood. In infancy, the proportion of fluids is much greater ; and in old age, less.

e. Weight, — The specific gravity of the blood is rather greater than that of water, being about 1.050. The serum is also denser than water. Its specific gravity is 1.025. The difference be- tween water and crassamentum is stated to be still greater ; the latter has a specific gravity of 1.12(>«

CHEMICAL PROPERTIES OF THE BLOOD.

78. The number of chemical substances dis- coverable in the blood itself, when subjected to th^ action of reagents, is very great, and yet th.Q

OF THE BLOOD. 83

ablest chemists have been unable to detect in it many substances which are known to exist in oth- er parts of the system, and which could only have got there through the medium of the blood. It is true that many chemical compounds may be ac- tually formed from ingredients contained in the fluid, at the moment of their being deported from it, in their respective places, and for this purpose some of the sanguineous constituents may be de- composed from one form, and recomposed into an- other at the same instant ; for different propor- tions of the same ingredients, and even different modes of union between the same proportions of the same ingredients, are known to result in com- pounds of very different properties.

Moreover, there are some substances found in the blood whose presence cannot be accounted for satisfactorily. Being simple bodies, they cannot be produced by combination of other matters, and the source whence they are derived remains un- determined. Such is the iron, which is now be- lieved to be the colouring matter of the blood. Recent experimenters have stated their belief, that in the blood of forty men there is iron sufficient to form a ploughshare.

79. Some experiments have been performed on the growth of plants, with a view of ascertaining, if possible, whether they would contain materials which could not possibly have been derived from the soil in which they grew or the water which nourished them. Seeds were planted in clean washed sand, sulphur, or some substance from which they could not be supposed to derive any extraneous matter, and were moistened with dis-

H

84 OF THE BLOOD.

tilled water. They were found, nevertheless, aftef arriving at considerable growth, to contain materi- als which must have been derived, in part at least, from some action of their vital powers, and could not have been obtained from without. So it is with the blood of animals. It contains materials whose soifrce is not understood ; and other sub- stances are produced from it, composed of matters of which no trace appears in it. There appear to be only three conceivable modes of accounting for this. " Either some of the bodies which we sup- pose to be elements, as, for example, oxygen, hy- drogen, carbon, sulphur, or phosphorus, are in re- ality compounds, and are decomposed by the pow- ers of life ; or these are capable of converting the elements into each other ; or, in the third place, there is a creation of absolutely new matter. The first of these suppositions is in itself by far the most probable."*

* This is the conclusion of some of the best physiologists. Perhaps the possibility of deriving those unexplained materials from floating particles in the atmosphere, so copiously inhaled with the air we breathe, has not been taken sufficiently into account.

OF THE BLOOD. 85

OF THE VITAL PROPERTIES OF THE BLOOD.

Secretion.

80. Under this head is placed the power which the blood possesses of eliminating from itself all the various materials necessary to form the differ- ent and numerous tissues of the bodies. When speaking of the capillary circulation, it was observ- ed that it was the province of that system to de- posite from the blood, in every part of the animal structure, the new material, which was to supply the place of the old, which had become deteriorated or worn out, and also to remove the latter. When we consider how very numerous are the tissues of the body, constituting the bone, muscle, nerve, ves- sel, cartilage, marrow, tendon, ligament, nail, hair, skin, membrane, &c., we are not more astonished that one fluid should contain the elements of so many widely different compounds, than that each should be deposited in its own proper place, and in none other. Nor is our astonishment lessened on reflecting also that a great many Jluids, all differ- ing greatly from each other, should be derived from the same identical source ; as the gastric juice, saliva, perspiration, bile, and mucus, the tears, humours of the eye and ear, &c. The process by which all these substances are given out from the blood is called secretion, which, in its original meaning, signifies a separation, as it was formerly supposed that the different matters existed already formed in the blood, and were merely separated from it by simple mechanical means, without un- dergoing any change in the act. Now, however, it is generally believed that during the process of

86 OF THE BLOOD.

secretion, some change, of a chemical nature, takes place in the substance secreted, proceeding on the supposition that it did not previously exist already formed in the blood. The process of secretion, strictly defined, may therefore be said to be " that function by which a substance is separated from the blood, either with or without experiencing any change during its separation."

81. What a curious and highly interesting chem- ical laboratory does the capillary system of circu- lation present to us 1 Without the aid of furnaces, crucibles, acids, or any other reagents, from one uniform, homogeneous fluid, by its wonderful pow- er, it decomposes the substance of that fluid, and recomposes the elements into a hundred other mat- ters. Nor is this all. Never, in a healthy condi- tion, does it make the mistake of elaborating a sub- stance in the wrong place. Muscle is not depos- ited in the place of bone, bone in the place of nerve, nor bile in the place of tears. But each little operator, knowing well its duty, with uner- ring precision deposites each part in the place where its Maker first designed it to be. No con- fusion or interference is ever known among them, though not a particle of diflcrence can be detected between them : each performs its appropriate work independently of all the others.

82. The function of secretion in many instan- ces developes a complicated fluid, and we gener- ally find in those cases an appropriate structure devoted to the operation ; a bofJy which is more or less of a rounded form, and hence called a Gland, Examples of such arc the liver, which secretes the bile ; the kidneys, which secrete the urine ; the

OF THE BLOOD.

87

sub-maxillanj (under the jaw) glands, which secrete the saliva, and so on. Each gland is supplied with a nunriber of little tubes to receive the secreted fluid, which unite into one larger tube, called the Duct^ which conveys the fluid to its destination. There is a large salivary gland placed behind and beneath the ear, called the Parotid Gland, which communicates with the interior of the mouth by a duct about as large as a small quill, through which it discharges its saliva during mastication. It is so situated that the working of the jaw, in chewing, compresses it, and forces the fluid along to mix with the food. Young people frequently are af- fected with a swelling of this gland, called mumps. Many persons, in the act of gaping, often squeeze the gland so suddenly by the wide distension of the jaws, as to eject forcibly a little stream of saliva di- rectly out of the mouth upon the book or paper be- fore them.

Fig. 26. There is a lit-

tle gland placed at the outer and up- per corner of each eye, which con- tinually exudes a small quantity of liquid, which runs over the front of the eye, keeping it always moist, bright, and clean, and discharging

itself through a 1, Parotid Gland ; 2, Duct for conveying i . .u •

the saliva into the mouth. ^^^^^ ^^ ^^^ ^""^^

H3

88 OF THE BLOOD.

corner into the nose. When mental emotions of a sorrowful character arise, these little telltales soon give notice of it by pouring out a more abun- dant secretion, which, being too copious to be car- ried off by the regular mode, overflows the eyes, and runs down the cheeks in the form of tears. These are called the Lachrymal Glands.

83. The operation of secretion, which we have thus seen to be a separation from the blood of cer- tain substances which are formed or produced at the moment of being deposited in their peculiar situations, is a process unlike any other known in nature. Almost every change wrought in the composition of the material w^orld, if within the reach of the chemist, is capable of being understood and defined by him. From the formation of a dew- drop, and its oxydizing action upon an exposed cambric needle, to the phenomena of a volcano, or the motion of the planets in their orbs, the scruti- nizing mind of the chemist and philosopher has dis- covered the true nature, or found a highly proba- ble cause. His mental vision has even penetrated into the long-concealed truths of many of the op- erations of animal and vegetable life ; but the real nature of the process by which the functions of se- creting organs are conducted, has hitherto eluded his grasp. The delicate capillaries carry on the decompositions, recompositions, solutions, and pre- cipitations in their laboratory, coextensive with the whole mass of the living frame, with the ease, quietness, and accuracy of the most expert manip- ulators, and man cannot discover the rationale of their processes.

The laws of chemistry, now so well established,

OF THE BLOOD. 89

which apply with unvarying uniformity to the molecular operations of inanimate matter, are sub-

. verted and disregarded in many of the functional actions of the living body, and especially of those of

' the secreting functions.

i The principle of life, superadded to the organi- zation of the animal, holds in complete control all the ordinary chemical rules, which, but for it, would very soon destroy the fair proportions and beauteous appearances of this frail tenement of the soul, and resolve it into noisome, invisible gases, and dark and shapeless masses of earth.

And what is this vital principle, and where does it reside ? are questions asked by every thinking mind. In an elementary work of this kind, it is not worth while to go into an extended notice of these topics ; and this subject is only adverted to here as the most appropriate place to make a re- mark or two upon the once supposed connexion of the life of the animal with its blood.

" For the Hfe of the flesh is in the blood,"* is a passage from Holy Writ very often quoted to prove that this fluid is the peculiar home of the vital prin- ciple. There are no doubt many, even at the present enlightened day, who, in their ignorance of

\ the laws of physiology, and of the multiplicity of

] different parts requisite to constitute a perfect ani. mal, remain contented with the view supposed to

' be unfolded to them by this solitary, unexplained text, and look no farther, believing they know all that can be taught them on the subject. Perhaps they become conflrmed in these ideas on observing that an animal will quickly die merely by losing

♦ Leviticus xvii., 11.

90 OF THE BLOOD.

a specific quantity of that precious fluid from a wounded bloodvessel, when they know, too, that in so short a time, no change in the solid structures of the body could have occurred adequate to such a result.

84. Life is not an accompaniment or an occu- pant of any one particular part or tissue alone, but every fibre and every drop of the system is in an appropriate degree endued with the principle. It is true, there are some parts which appear to be of no importance to the continuance of this incom- prehensible gift, inasmuch as the body may be de- prived of them, and no injury follow to its integ- rity ; still, every part, however obscure or unim- portant, while connected with the body, partakes of its vitality. If there is any one part which may be said to be pre-eminently the head and fountain of this principle, it is the nervous system; but it must not be forgotten that the functions of respira- tion, circulation, and secretion are, equally with the nervous system, necessary to the immediate, and that of digestion to the remote, continuance of life.

The scriptural text alluded to on the preceding page may doubtless, with implicit propriety, be construed as a precept uttered by the great law- giver, to the effect that the life of every animal will be destroyed when he is deprived of liis blood, and that the blood was the most convenient and proper to be offered upon the altar as a sacrifice. It cannot be understood to mean that the blood of an animal is the sole retainer of its life. That Moses entertained a more correct view of the sub- ject, believing that life was a gift or principle su-^

MOTORY APPARATUS. 91

peradded to the organization of the animal, is clearly demonstrated by the seventh verse of the second chapter of Genesis : " And the Lord God formed man of the dust of the ground, and breath- ed into his nostrils the breath of life ; and man be- came a living soul." The act of inspiring man with life is thus shown to be subsequent to his cor- poreal formation.

CHAPTER V.

MOTORY APPARATUS. PART I.

85. The utility of all artificial machines de- pends upon motion^ produced and modified in a va- riety of ways. The power which puts an engine or apparatus in motion is various in kind, and is derivable from many sources. In mills near water- courses, water is used as the moving power. In places where a stream of water is not accessible, this fluid, taken from wells or streams, may be converted into steam, which, in modern times, has become a very powerful agent. Wind is fre- quently employed to move machines. It is the means used to propel ships across the ocean, and, in defect of waterfalls, as the propelling force of mills for various purposes. One of these three is generally used where large and heavy machines

92 MOTORr APPARATUS.

are to be moved, as they possess very great mo- ving powers.

Sometimes motion is produced by letting a heavy weight fall slowly from a height, as in clockwork ; sometimes by the elastic force of bent wood or metal, or of compressed air ; and much more fre- quently than either is the power of brute animals and of men applied to similar purposes.

Recently a new motive power has been intro- duced, called electro-magnetism ; it is an invisible agent generated by galvanic action. It appears to be of some promise, but is yet in the infancy of its application. ^

The chief sources of power, therefore, applica- ble to machinery, are the force of running water, of wind, of electricity, of falling bodies, of men and other animals, and of steam. They are called motive powers. Their subserviency to the wants of man is almost infinitely increased by the exer- cise of human skill, in the changes given at pleas- ure to their amount and direction.

But not a single instance can be named in which an engine of any kind is able to set itself or keep itself indefinitely in motion. No artificial ma- chine has within itself the means of overcoming the resistance occasioned by the friction of its parts on each other, or, when once set in motion, of continuing in operation indefinitely. If it were otherwise, the invention of a "perpetual motion" might reasonably be looked for. A gristmill can- not turn without the aid of water ; a steam engine without steam ; a watch or clock without spring or weight, and so on.

If no artificial machine, then, can move its dif. ^ferent parts upon each other without the assist-

MOTORY APPARATUS. 93

ance of some motive power, how much less able must any engine be to move itself from one place to another. Suppose a cotton factory to stand on the banks of a river, and to be kept in motion by the water of the river running against its wheels ; if the river should become dry, neither the factory nor its machinery could change its locality, and go over the country to another river to find a water- power. The engine of a steamboat or a railroad locomotive is put in motion by the steam generated in the boiler ; but if the water or the fire fails, the engine and all attached to it must remain station- ary until the power is renewed.

But the machine which we are now studying differs from all others in these two most essential particulars. It possesses within itself the power of moving its different parts upon each other, and also of moving bodily from one place to another. The latter is called the power of locomotion. Both these faculties are possessed by animal bodies, and by some of them in a very high degree.

To produce motion in the animal machine, one particular substance is employed, which is so placed and arranged as to perform very conve- niently all the duties required of it. It is called Muscle.

86. Muscle constitutes all that part of the ani- mal body which is known as flesh, as distinguished from fat, bone, sineW) or cartilage ; it is the red or lean part of meat, and forms a very large por- tion of the bulk of the animal structure. In some animals it is white, as in the bodies of chickens and other birds, and in fishes.

The structure of muscle is very peculiar. When

94 MOTORY APPARATUS.

seen upon the table after being cooked, it will be observed to be composed of a great number of small strings or fibres, lying very close to each other, and bound up together. These may be easily separated from each other, and it will be found that each one is like all the rest.

87. In the recently dead body, the muscular fibres are soft, flexible, and easily cut or torn asun- der. They are then entirely devoid of any con- tractile power.

In the living body, on the contrary, they possess a high degree of contractility, i. e., they have the faculty of contracting or shortening themselves so as to bring the two ends nearer to each other, and this they can do with a great degree of force, and it is this force which constitutes, in fact, the power which all animals possess. In proportion to the contractile power of the muscles, is the individual said to be strong or weak.

The contraction alluded to is excited by a pe- culiar stimulus applied to the muscle by the nerves ; and when the stimulus is removed or ceases to op- erate, the muscle relaxes and returns to its former length. These two properties are the distinguish- ing characteristics of muscular fibre.

88. The muscles generally lie just beneath the skin, and surround the bones, especially those of the extremities, which are completely enveloped by them. As they are found near the surface, they serve to give much of that graceful contour which the body and limbs exhibit, and in many instances their prominent outlines may be distinctly traced. The strong "cords," as they are often called, which arc seen in the neck, ono on each side,

MOTORY APPARATUS. 95

running from behind the ear obliquely to the top of the breast-bone, are two muscles used for bend- ing the head to one side or the other, according as either acts. The full, rounded protuberance seen on the front of the upper arm, between the shoul- der and elbow, is a powerful muscle used to bend the elbow. The large swellings of the thigh and calf of the leg are formed chiefly of strong mus- cles, which are used mostly in walking, running, and similar exercises.

89. Each muscle is made up of a large num- ber of fibres, bound up together in a thin, strong casing, called the "sheath." The fibres lie par- allel to each other, and it is the contractions of the separate fibres, all acting at the same moment, that give to the muscle its great strength.

The muscles are all very distinct from each other, each one being enclosed in its own sheath, and easily separated from all other parts.

Each one is divided anatomically into three parts, viz., the hody, which is the middle portion, full and round, and the two ends, which are smaller than the body ; the latter gradually and gracefully taper to the extremities. Both ends are attached to some other body, and generally a bone. The fixed end is called the origin, and the moveable end the insertion, of the muscle. But a great variety is found in the forms of muscles, as represented in the cuts.

Figure 27 represents a form of muscle which, with shght variations, is one of the most com- mon. B is the body of the muscle, O the origin, and I the insertion. The ends of the drawing are not the ends of the muscle, but are tendons attached

I

86

MOTOUV APPARATUS.

to the fleshy fibres, whose use will be explained hereafter. '

Figure 28 represents an example of a muscle having a broad attachment at its origin O, and composed of a num- ber of bundles or sets of fibres, running in different directions, but all termina- ting at one point, the insertion I. The fibres in each bundle run parallel with each other, but the bundles do not. They not only run towards one point at the insertion, but they are twisted a lit- tle upon each other, like the strands of a rope. By muscles of this shape a great variety of motions may be pro* duced. If the bundles all act togeth- er, a straight movement will be given to the force ; but if only one set contracts, an oblique direction will result ; and a twisted motion also may occur. Such a form of muscle is found lying on the front of the chest. Its origin is at the ribs near the breast-bone, and its inser- tion is into the bone of the upper arm. Its use is to pull the arm across the chest ; and in the direction in which the arm moves in the different stages of its progress during this j action, it may be observed to ^ have a rotary or twisted mo- B -f tion. This is given to it by the successive action of the different sets of fibres of this muscle*

MOTORY APPARATUS.

97

90. Another form of muscle frequently found is that of the ring or circle. This is placed at the edges of the different orifices, as the mouth, the opening into and out of the stomach, &c. That which surrounds the mouth is just under the skin, and forms the outer part of the bulk of the lips. When it contracts it puckers up the mouth, as in

Fig. 29.

Muscles of the Face.

98

MOTORY APPARATUS.

the act of whistling, and when the mouth opens wide, it is fully relaxed.

Another circular muscle is the one which sur- rounds the eye, fig. 29. This is situated just beneath the skin of the cheek and eyebrow, and when its fibres contract the eyelids are drawn very tightly together. The most beautiful and delicate of all is the muscle which forms the Iris, the dark, variegated part of the ball of the eye. This is a perfect ring, having a round hole in the centre, called the pupil, or commonly, the " apple of the eye." It is remarkable also for its extreme sensitiveness, as it instantly contracts when ap- proached by a ray of light. The iris has two sets of muscular fibres, besides numerous bloodvessels and nerves. The first set of fibres converge from the outer circumference of the ring to the margin of the pupil, like radii, and hence are called the "radiated muscle." The second set is a ring of ^bres, which forms the inner edge of the iris and

Fig. 30.

1. The Iris magnified, seen from the front, showing the ra- diated muscle.

2. The same from behind, showing the orbicular muscle.

the margin of the pupil. It is called the " orbicu- lar muscle." When there is too great a quantity of light for the eye, the orbicular muscle contracts,

MOTORY APPARATTJS, 99

by which the pupil is nearly closed, and the light is partly excluded ; but in shady or dark situations, the radiated muscle contracts and the other re- laxes, by which the pupil is enlarged, and more light is admitted into the eye.

The action of this refined organ may be seen at any time in another's eye, by suddenly bringing a candle near it, when it will contract, and on re- moving it it will relax ; or even by covering the eye with the hand, and suddenly removing it in a bright day, the same effect will be produced.

91. The corresponding organ in some of the inferior animals has a different shape. In the cat kind it is an oval, with the greatest diameter from top to bottom. The pupil being the opening through which light enters the eye, in this species that direction of the hole enables it more easily to look upward as its habits require ; as in searching for prey in trees, &c. In grazing animals, as the horse and cow, the greater diameter is from side to side, as these require to embrace in their view as much as possible of a wide field. But man, re- quiring at times a view equally in every direction, has a perfectly round pupil.

92. Another form of muscle, and one which displays no less ingenuity than the others, is that of the pulley. Curious as it may seem, there are in the animal body several instances of this mechan- ical arrangement.

They are to be seen principally at several of the joints, especially those of the foot and hand. The muscles which bend the toes upward are placed on the front of, and are attached to, the bones of the leg. Long tendons are fastened to the lower ends of these muscles, commencing above the ankle. ^' *

12

100

MOTORY APPARATUS.

passing over the ankle joint to the top of the foot and toes. When the foot is stretched out far, the

Fig. 31.

View of the muscles which extend the toes and bend the foot. M, the common extensor muscle ; T, the tendons of the same muscle inserted iuto the toes; L, ligament binding the tendons ^Lown.

MOTORY APPARATUS. 101

muscles and tendons are nearly in a straight line with each other ; but as soon as the foot is bent up a little, the tendons make a turn, as it were, around a pulley.

When the muscles act very powerfully, the ten- dons would be forced up from their places were they not bound down by strong ligaments running across them. These ligaments act like small cords, and are tenacious enough to keep down the tendons, however powerful may be the action of their muscles.

The same arrangement, though forming a more complete pulley, is found in the muscles and ten- dons which bend the fingers ; but a description of these will be found in the chapter on the " Hand."

93. The most delicate and beautiful of all the instances of the pulley, to be found in the body, is one placed within the orbit of the eye.

Every observing person must be surprised at the great variety and number of the motions of the eyeball, although he may be unacquainted with its anatomy ; but that surprise will be rather height- ened than diminished when he becomes acquainted with the means by which it acquires such great facilities of movement.

The following figure presents a very clear view of the arrangement of the different little muscles, whose contractions communicate to the eye its motions upward or downward, to the right or left, or towards either of the four corners.

The muscles which move the eyeball are six in number, four of which are called " straight," and two "oblique muscles." Of the latter, one is the " great," and the other the " lesser oblique" (fig. 32).

102

MOTORY APPARATUS.

Fig. 32.

Side view of the muscles of the eye in their natural position. abed, the four straight muscles (a is turned up to prevent the others from being hidden) ; c, the great oblique muscle ; /, the optic nerve. (The second oblique muscle is not shown, but its situation may be inferred.)

The actions of the straight muscles may be un- derstood from the figure ; according as each con- tracts, the front of the eye is turned upward, down- ward, or to either side, in a perpendicular or hor- izontal line. Hence these muscles derive their appellation of "straight." But to produce the ob- lique motions of the eye is the office of the tw3 oblique muscles.

MOTORY APPARATUS. 103

94. The "great oblique," or pulley muscle, "is one of the most interesting in the body, and, as a marvellous work, offers a brilliant example of the mechanical wisdom of the Creator, demanding our closest attention." It arises from the margin of the aperture in the bottom of the orbit,* which transmits the optic nerve from the brain to the eye. Thence it runs forward, slantwise, to near the upper front edge of the orbit, where is fastened to the bone a cartilaginous ring, through which it passes like a rope over a pulley, and, turning back- ward, it increases a little in width, and is inserted into the back part of the ball of the eye. "When it acts, it rolls the eye about its axis towards the nose, and, at the same time, draws it forward and turns the pupil downward." The motions of the eye produced by this muscle are very extensive, and could not have been effected except by a muscle longer than could lie straight in the orbit, and hence we have a reason for the display of this beautiful mechanism.

95. Some muscles are found of great length ; some very short, with very long tendons ; some are broad and flat, some round, and some nearly square, and others hollow. But all are made of the same material, and their contractions and relax- ations are produced in the same manner. Every motion in the hody, howxver powerful, extensive, minute, or delicate, is the result of muscular con- traction.

As the number and variety of the movements of the body are incalculable, the number of distinct

* The bony case or " socket" in which the ball and appara- tus of the eye are securely placed.

104 MOTORY APPARATUS.

muscles, it would be supposed, must be also great. There are in the body 436 muscles, all distinct and separate from each other ; every one of which is capable of producing at least one motion, and va- rious combinations of few or many of them may and do give rise to the infinity of movements from which the animal body derives its wonderful flex- ibility.

96. The study of the nature of the contractile power of muscles does not come within the scope of a work on the mechanism of the frame, but an out- line of the subject, as far as we are acquainted with it, will not be inappropriate. The substance of a muscle has been stated to be divisible into smaller portions or filaments, called fibres. These fibres are as distinct from each other as are the bundles of them, or the muscles themselves. The fibres of some muscles are comparatively coarse, and others are very fine ; but all, when minutely exam- ined, are seen to be composed of an arrangement of " globules," united with each other, which bear a strong resemblance to the globules of the blood.

Each muscle is supplied with a nerve coming either from the brain or spinal marrow, and thus, of course, is connected with the mind, which in- habits the brain. Immediately after the nerve enters the muscle, it divides into innumerable ram- ifications, each of which goes to supply one of the millions of fibres composing the muscle.

The nerve is the medium of communication be- tween the mind and the muscle, and through it is transmitted the stimulus of the will, which causes the muscle to act. For instance, when there is occasion to raise the arm, the desire or will arises in the mind, and is sent through the appropriate

MOTOR Y APPARATUS. 105

ne!*ve to the muscle which it supplies ; the will thus sent is the peculiar stimulus which causes the muscle to contract. Each fibre contracts inde- pendently of all the others ; but as they are all sup- plied with the stimulus at the same instant, each one beino; furnished with a filament of the same nerve, they all contract simultaneously ; and al- though one fibre has but a trifling amount of pow- er, the aggregate of the whole produces the im- mense strength which some muscles are known to possess.

The nature of the stimulus which is given to the muscles by the nerves never has been, and prob* ably never will be, ascertained.

97. The muscles of the system are divided into two large classes, distinguished by the cue being entirely under the control of the will, .^lence call- ed Voluntary, and the other equally beyond its control, and called Involuntary. TAe former we may move or not, as we please ; ^tmong them are the muscles of locomotion, of th^ voice, of the eyes, &c., while the latter class comprises the muscles of circulation, as the heart ^^-nd bloodvessels, those of digestion, and a few others. The muscles of respiration belong exclusively to neither class ; for they are so far voJUKcary, that their action may be suspended by t/ic will for a short time, but it is im- possible for a person altogether to stop their ac- tion, oiherwise suicide might be committed merely by restraining respiration, in other words, produ- cing suffocation. They are, therefore, to be con- sidered as both voluntary and involuntary ; the former in a much less degree than the latter. The (surpassing wisdom of this distinction between or*

106 MOTORY APPARATUS.

gans whose minute structure exhibits not the slight- est trace of difference, is clearly apparent. The involuntary muscles are those which are intimately concerned in the continuance of life ; and if they had been, like those of the hand or the foot, placed under the guidance and care of the wayward minds of their owners, how soon, amid the engross- ing occupations of time, or from the wicked deter- mination of the self-destroyer, would their actions be deranged, forgotten, or neglected, and life on the instant be forfeited.

98. Not the least astonishing among the facul- ties of the muscular structuro is the velocity of movement of which it is capable. A striking ex- emplifi'^ation of this may be seen in the rapid ac- tion of fae muscles of the fingers in playing upon musical instruments. But a more remarkable ex- ample are "rhe muscles connected with the organs of speech, wh^^re, in rapid enunciation, the number of distinct contiactions that take place in order to form certain comiinations of vocal sounds is very great, each word, oi, rather, each syllable, requi- ring several contractioas, which must succeed each other in rapid succession, with proper intervals be- tween them." In the actitvn of the fingers in the former mstance, the contractions are generally greater in extent, and, therefore, rnu^t proceed with proportionably greater velocity, altho'igh they do not succeed each other so rauidly as those of the vocal organs.

MOTORY APPARATUS. 107

TENDONS.

99. The substance of muscular structure, when closely examined after death, is found to be soft, possessed of very little tenacity, or easily torn in pieces. So very delicate is its texture, that a muscle which, in the living body, would be able to sustain a weight of 100 pounds by its contractile power, would be unable, when deprived of life, to hold a weight of ten pounds. That is, if it were separated from the body, and it should be held in the hand by one end, and ten pounds were attached to the other, the muscle would break in two. From the invisible and incomprehensible principle of life, €L substance derives an almost incalculable power, of which in a few moments it may be deprived and be rendered as pon^erless as an equal bulk of un- twisted flax, and yet not a vestige of alteration, chemical or njechanical, is perceptible in its struc- ture. But. cenacious as its fibres may be during life, there is a limit of power beyond which it woula be unsafe to try it. There are some situa- tions, however, in which it would be hazardous to «xert a moiety of a muscle's strength, were it un- furnished with efficient protection. Such a situa- tion is that where a strong muscle is attached to a bone. Bone is a material very different from muscle in its structure, and is the same in proper- ties before or after death. It is hard, firm, strong, and inflexible, and somewhat brittle, and possesses none of the softness and delicacy of muscle. A bone, therefore, will endure the application of a much greater force than muscle without injury.

108 MOTORY APPARATtrS.

100. When a muscle contracts, its ends are ap* proximated, and, of course, one of them at least must be moveable ; therefore, whatever substance is attached to the moveable end, must move with it when the muscle acts. The substance upon which the muscle exerts its power is generally a bone, and the motion is brought about through the intervention of a joint.

But it is very rarely that a miascle is found fas- tened directly to the substance of a bone ; the or- gans in many instances are required to exert such great strength, that the strongest attachment pos- sible between the two would be too feeble, in con- sequence of the softness of the muscle, and a sep- aration would be the result. For example, let us take the muscles of the calf of the leg and the heel-bone. These rnuscles are used in walking", running, leaping, and such exercises, and being connected with that bone, when they contract they raise the heel and throw the whoi^, body forward. "When, as we often see, a weight of one or two hundred pounds, carried on the head or in the hands, is added to the weight of the bodj, these muscles have to exert extraordinary power, and the slender connexion which only could be made directly between their structure and the bone would be insufficient to sustain it ; a painful and inconvenient separation would ensue, requiring weeks of cautious repose for the reparation of the injury.

Most happily, in every requisite situntion, the an- imal frame is provided with a preventive against such a distressing event. This is the intervention of a third substance between the bone and muscle^

MOTORY APPARATUS. 109

which possesses properties most admirably adapted to its offices. It is called Tendon, and goes com- monly by the name of sinew.

101. Tendon is a very peculiar substance, un- like any other in the body. In texture it more nearly resembles cartilage, but possesses no elas- ticity. In strength it is scarcely inferior to bone, yet it is perfectly flexible ; it is much denser and firmer than muscle, but is totally void of contrac- tility, and is insensible, having no nerves. It is generally found in the form of long, slender strings, but frequently is observed in broad sheets,* and short and thick cords. It does not appear to lose any of its tenacity when deprived of life ; and on account of its immense strength and great length in some inferior animals, it is often used by Indians for the manufacture of bowstrings and for other purposes, for which it is well adapted also by its smooth and glossy surface.

102. The longest tendons in the human body are in the hand and foot. The muscles which bend the fingers are placed on the arm between the elbow and wrist ; they do not go beyond the wrist joint, and their power is exerted upon the fingers by means of slender and strong tendons, which pass over the joint (confined down by a lig- amentous band lying across them) and through the palm to the difierent joints of the fingers. All the immense force which is often exerted by the hand in grasping and pulling, must, of course, be borne by these fine cords ; but I know of no in- stance in which they have ever given way. The

* In this form it is called, in some parts of the country, by the singular name of Packwax.

110 MOTORY APPARATUS.

muscle or the bone is more likely to yields On the back of the hand, the tendons which assist to extend the fingers may be distinctly traced, one going to each finger and thumb.

The most delicate tendons are to be found at- tached to the minute muscles of the eye and heart.. They there appear like slender threads of glossy white silk (figs. 3 and 4).

103. The flexibility and tenacity of tendon are the two qualities which render it appropriate as the medium of union between a muscle and a bone. At its muscular end its fibres are closely and strongly interwoven with those of the muscle, in such a manner that it is next to impossible to sep- arate them clearly, even with a knife. They so gradually slide into, and become incorporated with, each other, that it is difficult to tell where one be- gins and the other ends. The same remarks are applicable to the end which is attached to the bone. Numerous filaments of the tendon glide in between the laminae of bone, round which they intimately entwine themselves ; and so firm is the union, that an effort to separate them results in a rupture of the tendon or bone before the connexion can be severed.

104. Another very important advantage derived from the use of tendon is, that m,uch space is saved and a graceful form given to the structure of the limbs. Let us compare, for instance, the shape of the leg as it is, with what it would be, deprived of its tendons. We find the great muscles which form the calf tapering gradually from their thick- est part down to a much smaller compass, and terminating in a strong tendon, which unites it to

MOtORY APPARATUS. Ill

the heel, and through which it transmits its power. By thus concentrating the contractile force of the muscle, not only is there a diminution in the quan- tity of matter in the soft parts without loss of pow- er, but the smaller tendon requires far less surface of .bone for its attachment, thus also lessening the size of the heel and reducing the weight of the body.

Suppose, now, the muscle, instead of diminish- ing, had continued down to the heel of as large size as at the calf; not only would ihe ankle have pre- sented awkward and inconvenient dimensions and form, but the heel-bone must have been made five or six times its present size to have presented suf- ficient surface for the attachment of the muscle. A more striking exemplification still may be seen in the muscles and tendons of the hand. Suppose, instead of the graceful tendons, the muscles of the arm had continued their course over the wrist, and with undiminished bulk had been attached to the fmgers ; not merely would we have been deprived of the aid which their present shape affords us in innumerable delicate manipulations, but in many of the powerful operations to which they are now safely adapted, the muscles would have been liable to numerous painful disorders, from which the in- sensible tendons are totally exempt. We find, therefore, not only symmetry and convenience of form and facility of motion with concentration of strength, but also a great diminution of the weight of the whole body, derived from the present ar- rangement, all of which would be lost in the re- verse condition.

K2

112

MOTORY APPARATIT9.

THE LEVERS.

105. As complete as any of the mechanical coiv trivances of the body are the Levers. In the sci* ence of mechanics, levers are divided into three kinds, depending upon the relative situation of their three points, viz., the power, the weight, and the fulcrum. The instrument, in its plainest form, is merely a straight, stiff bar ; and its power, which, under the most favourable circumstances, is very great, depends upon the relative distances o-f these three points from each other.

106. The Jirst land of lever is that in which the power is at one end, the weight to be raised at the other end, and the fulcrum, or point on which the lever rests, is somewhere between the twa.

Fig. 33.

The common crowbar and the handle of a pump> are instances.

107* In the second kind af lever, the power is

Fig. 34.

MOTOR Y APPARATUS. 113

at one end, the falcrum at the other, and the weight between the two.

The wheelbarrow and nut-crackers are in* stances of the second kind.

The difference between the first and second kinds is merely that the fulcrum and weight have changed places.

The lever has two arms, each commencing at an end of the lever and extending to the intermediate point ; and the power derivable from the use of ei- ther of these kinds depends entirely upon the dispro- portion in the lengths of the two arms. That is, if the long arm is ten times the length of the short arm, a power equal to one pound will be equal to a weight of ten pounds ; if the long arm is twenty times longer than the short arm, a power of one pound will balance a weight of twenty pounds.

108. The third kind of lever has still a different arrangement of the three points. The weight is at one end, the fulcrum is at the other, and the power is placed between the two.

Fig. 35.

In this kind of lever there is not only no gain of power, but there is a great loss of it; there is^ however, a great advantage derived from its use^ viz., the gain of velocity in the movement of the weight. A ladder, while being raised against a house, constitutes a lever of the third kind. Ther

114 MOTOR V Ari'AKATUs.

foot of the ladder is the fulcrum, the power is ap- plied near the foot, and the ladder is itself the weight.

109. The lever is among the most powerful of mechanical instruments, and its three varieties of form render it applicable to a great many pur. poses wherein great force or great velocity is re- quired, while its unequalled simplicity of construct tion recommends it in almost every situation. In every artificial machine, a great aim of the in* ventor is to bring in the aid of the lever whenever he can, as from it he can generally derive a greater power in a smaller compass and with less cost than from any other of the mechanical contri* vances.

In the construction of a machine so complex, and uniting in one whole so great a number and variety of separate parts as does the animal body, it may readily be believed that its Omniscient ar- chitect, though possessing unlimited means, would not be less wise than man, and fail to employ those measures which would accomphsh his ends in the most simple, most economical, and most powerful manner. If we trace the impress of his divine mind through the universe, we are everywhere surprised not less at the immensity and power of his operations than at their simplicity. The union of strength and simplicity is nowhere more strikingly exemplified than in the erection of this mortal habitation of our souls, " the house we live in."

Conclusive evidence of this is found in the ap- plication of the lever to every part of the bony structure where it can possibly be applied with

MOTORY APPARATUS.

115

advantage, and, moreover, in the selection of that kind of lever for each particular position in which it is evident it should have been preferred before the others.

110. We have in the body several instances of each of the three kinds of lever.

Of the first kind, an example is presented in the forward and backward motions of the head. The scull, in the erect posture, rests upon the upper bone of the spine, and is thrown backward or forward by appropriate muscles placed at the back of the head and neck, or at the front under the chin. If an imaginary line is drawn along the base of the scull from the chin to the back of the head, it will represent the lever. The spine on which it rests is the fulcrum, the power (the muscles) is placed at one end or the other, as the head may be moved one way or the other, while the weight is the head itself.

111. Of the second^ kind, a striking instance is seen in the foot as ft is used in walking. The

Fig. 36.

116 MOTORY APPARATUS.

lever is the foot itself, from the heel to the toe ; very irregular and uneven in its form, yet, to all intents and purposes, acting in the exercise men- tioned precisely as a second kind of lever.

In figure 36 we have a view of this arrange- ment. P is the point where the muscle, M, of the calf of the leg is attached by its tendon, and where it applies its power. F is the fulcriwi, the point on which the foot rests when the heel is raised ; and W is the weight, which in this case is the whole body supported by the leg.

It will be perceived, that in this arrangement the weight is nearer the power than the fulcrum ; in other words, what is generally the long arm of the lever is here made the shorter arm, and what is usually the short arm is here made the longer. Tli^ inference to be deduced from this fact is, and very properly, that there is a considerable loss of power ; for it will be seen, by a glance at the fig- ure, that if the weight had been placed nearer the fulcrum, less power would have been required in the muscle to raise the heel. A muscle of less size would have been sufhcient to perform that duty, or, what is equivalent, the same muscle could have done more work. But we may also see that the power which appears to be lost is only sacri- ficed for the attainment of an equally important end, that is, velocity. Had the leg been united to the foot at a point nearer the fulcrum, it would have required a much longer contraction in the muscle to raise the leg through the same distance, which would have made necessary a much longer muscle, and caused a loss of time in the contrac- tion M'hich would very poorly have compensated

MOTORY APPARATUS. 117

for the economy of muscular strength. Besides, the present symmetry of the limb would have been lost, and the necessary exercise of running great- ly impeded. What, therefore, is lost in power, is gained in velocity.

112. Of the third kind we find several remark- able and beautiful examples.

The instance generally adduced is one which, in a striking degree, illustrates all the losses and all the gains in the employment of this mechanical power. This is the " forearm," the part below the elbow. The muscle which bends the elbow-joint and raises the hand towards the head, lies in front of the upper arm, and forms, when the arm is bent, the large fleshy ball, apparent in all individuals, just above the elbow. The origin (O, fig, 37) of this

Fig. 37.

muscle is by two heads (hence called the biceps), formed of long tendons, T (fig. 27 is a representa- tion of it), which are fastened to the bones of the shoulder. Its insertion, I, is also by a strong tendon into the large bone of the forearm, near the elhow^

118 MOTORY APPARATUS.

joint. It of course has to pass over the front of the joint.

The arm and hand here constitute the lever. E is iho fulcrum at the elbow- joint. B is the body of the biceps muscle, attached by a strong tendon at I, and forming the poioer, while the weight, W, is the hand and its contents. When the muscle con. tracts, the lower end must move and take the bone with it. The bone of the upper arm being fixed, those of the lower arm turn upon it at the joint, and the hand is raised in a curved line.

113. A more disadvantageous arrangement as regards the amount of power necessary could not have been contrived. For when the arm is fully extended, at the first contraction of the muscle its power is exerted in nearly a direct line with the bones, and almost all its force is employed to over* come the obstacle presented by their position ; the nearer a right angle, the more advantageously does the muscle act upon the bones, and vice versa* But in the most favourable position there is a great loss of power. To repeat, however, what has been before said, in other terms, " we shall fmd it to be a general fact, or, as it is termed, a law of the an* imal economy, that muscular power is always sac* rificcd to convenience. Had the object been to raise the weight with the least possible; power, the muscle would have been j)laced on the forearm, and the tendon inserted into the lower part of the shoulder-bone ; but in this case the awkwardness ' of the limb would have much more than counter- balanced the supposed advantage of the saving of muscular power. The remark applies with still greater force to the fingers. Had the present or-

MOTORY APPARATUS. 119

der of muscles and tendons there found been re- versed, and the flesh of the muscle been placed on the fingers, the hand would have been ahnost use- less from its clumsy form."

114. Another important acquisition in this dis- tribution of the points of the lever is the great ve- locity.

By referring to figure 37, it will be made evi- dent that the hand will move through a far greater space than the end of the muscle in the same time. In carrying the hand from the most extended posi- tion to the shoulder, a distance of at least three feet in an adult, the muscle is not shortened more than two or three inches. Rapidity of movement is one of the most valuable aids we possess in com- mon with most other animals, and we acquire it in this perfect manner. Paley judiciously remarks, " that there are many more cases in which it is useful to raise a small weight rapidly than a large one slowly.'*

115. Another instance of a lever of the third kind is the leg. The muscle which throws the leg and foot forward lies in front of the thigh, and in size is commensurate with the great power re- quired of it. But in its attachment it presents an interesting exception to the general mode. In the place of having a long tendon to go over the knee- joint to be fastened to the upper end of the leg, we find at the front of the knee a round, rather flat, and moveable bone, calkid the " knee-pan" or pa- tella, which is plainly discernible. This bone serves a double purpose. The knee-joint, from its size and position, is more liable to injury than al- most any other ; and following the universal rule of

XA

120 MOTORY APPARATUS.

an all-wise Creator, that the most protection is ex- tended to the part most exposed to accident, this bone is placed as a strong shield, directly in front of this very important point, to secure it against the action of injurious agents ; an end attained far more effectually than if its place had been supplied merely by the tendon of the muscle. But it offers no impediment to the action of the muscle ; on the contrary, its position and mobility greatly assist it. The tendon of the muscle is attached to its upper edge, while another tendon unites its lower edge with the bone of the leg. When the power of the muscle is exerted, it is transmitted through this bone more efficiently than could have been done with a long tendon running over the joint.

116. " Amid so many examples, where muscular power is expended for the purpose of producing some important benefit to the system, there are a few instances of a contrary kind, where • the parts are evidently formed to assist muscular action. The heads of the bones into which the tendons are inserted not unfrequently swell out into rounded projections, by which means the muscles act upon the bones at a less acute angle." An example of this is the heel, which projects far back beyond the line of the leg, to give a better opportunity to the muscles to be attached and to act. (See fig. 36.) Another striking example is in the elbow (fig. 38).

The point on which the elbow rests when we lean on the table is a projection of one of the bones of the lower arm. To this is attached the tendon of a large muscle, which lies on the back of the upper arm, and whose office is to extend the arm. It can do this with great force, in which it

MOTORY APPARATUS.

121

is materially assisted by this projection, as it en- ables the muscle to act upon the bone more at Fig. 38. a right angle, which

is the most favourable position. This pre- sents us, also, with an- other good instance of the chief advantage of the third kind of lever, quickness of movement in extending the arm, as in throwing a stone. The general princi- ple, however, which has been alluded to, still holds good, "that the quantity of power employed appears to have been no object in the construction of the body, but that it is al- ways sacrificed, with- out any reserve, either to general conveni- ence, to symmetry of form, to the gaining of velocity, or to the sa- ving of the extent of contraction." The few instances to the contrary which might be adduced, can only be regarded as exceptions to the general rule ; exceptions founded in the same surpassing wisdom that has erected the principle.

122 MOTOKY APPARATUS.

CHAPTER VI.

MOTORY APPARATUS.

PART II.

THE BONES AND JOINTS.

117. The muscles, the organs hy which motion is produced, having been considered, the next sub- ject to be studied is the means through which the former are enabled to operate, and the parts which are moved by them. These are the Bones and the Joints.

In this study we shall find instances no less nu- merous than in other structures of the body, in which our attention will be arrested by the display of surpassing ingenuity evinced in the construction of a framework in every respect surprisingly ef- ficient.

The anatomical divisions of the skeleton are three, viz., the Head, Trunk, and Extremities. The first is well known ; tiie second embraces all *the parts immediately attached to the spine, except the head ; and the third comprises the shoulders, arms, and legs, or the upper and lower extremities. The trunk (fig. 39) consists of the spine, a a; the ribs, r r ; the sternum, or breast-bone, x x ; and the pel* vis, s s ; w, the middle bone of the pelvis, called sacrum ; this supports the spine ; y, the collar- bone ; h, the humerus ; c, the elbow-joint ; d, the radius ; e, the ulna ; f, the wrist ; g, the phalanges of th(3 fingers ; h, the iiip-joint ; i, the femur ; I, the patella, or knee-pan ; k, the knee-joint ; m, the tibia;

motory apparatus,

123

n, the fibula ; o, the ankle ; p, the phalanges of the

toes, _

Fig. 39.

Front view of the Skeleton.

L2

Fig. 40.

"aHALtV p.

g?Ct(H^-

Rear view of the Skeleton.

MOTOR Y APPARATUS. 125

The shaded outline (fig. 40) represents very ac- curately the fleshy bulk of the body, and the posi- tion of the bones within,

118. In looking at the skeleton (which is the framework of the body, upon and around which all the other parts are built), it seems as if every quality of matter, which could possibly be usefully employed, had been brought together and blended with each other in the most harmonious propor- tions, so as to produce a structure capable of sus- taining, in the most perfect manner, all the various uses to which it is put, and of successfully resist- ing the innumerable destructive influences to- which it is continually subjected. We find hardness com- bined vfiih toughness ; strength and firmness with a great degree of compactness ; and an admirable ar- rangement, by which the sizes of individual bones^ or of parts of a bone, are increased in hulk when required, without any addition to their weight or diminution of their strength.

119. The substance of bone is the hardest of all the materials composing the body. Its chemi- cal composition displays a blending together of two totally different materials, unlike in both their physical and chemical properties ; the one being hard and hrittle, while the other is soft, tough, and very flexible; neither of which qualities, independ- ently, does a healthy bone possess. By the union of these abstract properties in proper proportions, however, there results a condition of stiffness and[ toughness, without flexibility, peculiar to bone, giv- ing it its high value. It will be manifest, on the least reflection, that flexibility would be totally im- proper in bone, having to bear, as it does, the en*

126 MOTOR Y APPARATUS.

tire weight of the body, and forming all the joints. And yet we find this property of matter very con- spicuous in one of the two constituents of bone when separated from the other ; it becomes neu- traUzed by the combination of the two, and forms, with the brittleness of the other part, the hardness and strength so remarkable in bone.

120. The two constituents of bone alluded to are the animal portion, and the earthy or mineral portion. The former is the tough, flexible part, and the latter the brittle part. Tiie two are very easily obtained separately.

The animal portion may be obtained by putting a clean bone of any animal in a vessel of dilute muriatic acid. In a few hours, on removing it from the acid and washing it carefully with water- it will be found to have lost its characteristics c bone, to be soft and of a yellowish colour, but yet to retain with perfect exactness the shape and size of the original bone. It may be tied in a knot (if a long bone) without breaking, to exemplify its toughness and flexibility.

Fig. 41.

Bone in a knot.

MOTORY APPAEATUS.

127

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\tl:

P.

m

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The action of the acid has been to dissolve the earthy portion, for which it has a strong affinity, and separate it from the animal portion, which it has no power to affect.

121. The earthy portion is obtained by putting a sound bone into a charcoal or anthracite fire ; the great heat consumes the animal substance of the bone, and dissipates it entirely in vapour ; but it has no material effect upon the mineral part, which may be taken from the fire when the smoke and vapour have ceased to be given off.

This part will be found to be white, and also to be of the same form and size as the original bone. It is then so brittle and tender that pieces may be taken out with the finger nail, and it may be crum- bled between the fingers.

It has been said that each of these portions, when separated from the other, retains the precise form and bulk of the bone from which it is derived. This will convey to the observer substantial proof of the extent to which the union of the two is carried in the formation of the complete bone. Every particle of each bone con- Portion of aTone tains its due proportion of each calcined. constituent, so that the whole bone is alike firm and strong in every part.

128 MOTORY APPARATUS.

122. But it is well known that the proportions of these two parts are not always the proper ones. In some individuals, the bones possess a larger share of the earthy matter, and in some there is too great a quantity of the animal matter* A preponderance of the former gives to the bones too much brittleness, and renders them very liable to be fractured, while, with a superabundance of animal or deficiency of earthy substance, the bones become too flexible, and yield under the weight imposed upon them, producing crooked and de- formed limbs or bodies.

Both these conditions are produced by disease, when they are found in middle-aged adirlts.

123. There are, nevertheless, variations in the proportions of these two parts almost continually occurring in every healthy individual, which are widely different in their extremes, and given to us by an inscrutable superintending power for the most beneficent purposes. The variations are found at the difierent ages of the individual.

In infancy the bones possess a much larger pro- portion of animal than of mineral substance ; in fact, when the foundation of a bone is first laid, it contains almost no earthy matter at all, being com- posed almost wholly of what very closely resembles cartilage. The bones in infancy are, therefore, not stiff and hard, as in after life, but are considerably yielding and flexible. But as the child grows, the bones become gradually more solid and firm, and more capable of supporting its body and of sus- taining the action of its muscles.

Tills is a beautiful provision for protecting the infant against the consequences of its own helpless-

MOTORY APPARATUS. 129

ness. It would be useless to give perfect bones to a child that has not muscular strength enough to support its own body, as it could have no employ- ment for them ; and in its early attempts to walk, every time that it should fall upon the floor or against a table, they would be in danger of frac- ture ; or even when still younger, it should acci- dentally fail from a bed or the nurse's arms, broken bones would be its continual misfortune. Such un- necessary perfection of structure, therefore, is not found in Nature's wise code of laws. As it now is, a young child may meet with such accidents every hour in the day ; it even may fall upon its head, and receive no permanent injury. The bones, being composed chiefly of animal substance, hend before the blow, without breaking, and by their elasticity immediately recover their proper position and form.

On account of this disproportion of the two con- stituents of bone in infancy, caution is always ne- cessary, in rearing young children, to avoid too early a pressure upon any of their bones, particu- larly those of the lower extremities. From the readiness with which the bones will bend under pressure, the weight of the child's body is suffi- cient to produce a permanent alteration in its shape.

For the same reason, the habit which some moth- ers and nurses have of carrying the infant always upon the same arm, or laying it in one position, should be carefully guarded against ; many a spine has doubtless been crooked for life by that repre- hensible practice, and I know at least one instance in which a striking and ugly alteration in the form of the scull has been caused in the same way.

130 MOTORY APPARATUS.

One side is flattened considerably by its constant pressure against the mother's arm when young and soft.*

124. The bones do not become entirely solid, that is, every part of the bone does not receive the exact proportions to form the strongest material, until the age of puberty. They retain a certain degree of their flexibility and softness, but which gradually diminish until the strength of the muscles requires a firmer substance for attachment, and they then receive the proportions necessary to con- stitute levers of the most firm, durable, and un- yielding character. They are then able to endure all the force which can be put upon them by the individual, and it is only when an extracrdinarily severe blow is given them from without that they will break.

125. In old age we find another and a very dif- ferent change in the composition of bone. Instead of either the yielding structure of the youth, or the firm, unyielding material of vigorous manhood, we have, in going down the vale of years, a skeleton

* Doubtless many other instances of like character might readily be found ; and it is a matter of authentic history, that some of the American Indians are in the practice of aJtering the shape of their heads, to suit their ideas of beauty. They ac- complish it by compressing the children's sculls when imper- fectly developed, by applying liat pieces of wood against them, and confining them in their places by tight bandages. The fashumable shape is now said to be that of a quadrangular cone. The form of the brain must of course be altered to correspond "With that of the scull. It is in this manner, also, ihal the Chi- nese produce such horrible deformities of tlie feet of their fe- males. 'I hesc practices appear to us as not only ansurd and., ridiculous, but as wickedly lampering with the order of** Heav«w en's first law," and yet are neither of them more ol)noxious to these imputations than the present civilized practice of compress- ing the chest.

MOTORY APPARATtrs. 131

which has lost much of its firmness and strength, and which, in the place of toughness, has assumed a hrittle character ; a condition the very reverse of that of childhood.

The bones become strikingly deficient in the animal matter, giving a preponderance to the min- eral substance, a change which arises from the general decay of the system. The earthy part of bones, being the most durable and less liable to de- cay, is more permanent, and partakes less in the changes of adult life than the animal portion ; and hence, when old age creeps on, it is less influenced by the absorbent system ; the animal part is more readily removed, and, from the inactivity of the cir- culation, is not proportionately restored. Hence the deficiency of this part of the bony structure. There is, fortunately for the aged, a correspond- ing deficiency of muscular energy, otherwise their bones would be unable to bear the force which might be exerted upon them, and, from their fragil- ity, would be too readily broken ; and it is known by every surgeon, that an old bone, when broken, is far more difficult to mend than a young one. The proper ratio in the diminution of the firmness of the bone and the strength of the muscle does not, however, always exist ; the bones sometimes grow very brittle, while the muscles continue strong, and accidents may happen to a bone by too great an I exertion of the muscular strength. A well -authen- ticated case is on record of an old gentleman who, from this disproportion of strength between his muscles and bones, actually broke his arm in the uct of pulling on his glove.

126, On the other hand, cases are sometimes

M

1S2 MOTORY APPARATUS,

met with in middle age, in whose osseous system there is not a due proportion of the earthy con- stituent. While the muscular system has arrived at its condition of maturity, and requires for its free and complete action a strong and firm bony structure to operate upon, the latter does not cor- respond in hardness, but, in consequence of this de« ficiency, fails to present a proper resistance to the power of the muscle, and bends before the force applied to it. This unnatural condition is owing to the want of a proper balance in the vital actions of the system ; the digestion of the food, the circu- lation of the blood, and the absorption of the de- cayed material of the body, do not go on in their proper relative ratio.

Such unfortunate persons are readily known by the great degree of deformity of their limbs, and by the facility with which they become distorted without fracture.

To so great an extent does this diseased condi- tion occasionally exist, that some long bones may be bent entirely double, or curved into a circular form.

" On dissection of those who have died, all the bones, except the teeth, have been found unusually soft, so that scarcely any of them could resist the knife, and the bones have been found to contain a great quantity of oily matter and little earth.'*

Fortunately for mankind, it is a rare disease.

MOTORY APPARATUS. 13S

SHAPE OF BONES.

127. In examining the mechanical structure and arrangement of the different parts of the skeleton, we may observe a very great variety in the shapes of the bones ; and every one must be struck with the perfect adaptation of each bone to its situation and its uses. Thus we find in the arm, and thighs and leg, long bones of cylindrical form, with their ends enlarged to form strong joints. The ribs are also long bones, but they are very much curved and twisted. Then we find some bones very broad, flat, and thin, such as the bones of the scull, the shoulder blades, and the hip bones. Again, some are thick and square, or cubical, as those of the ankle, which has seven, and the wrist, which has eight bones. Others are found of which no word will express their shape, being so exceedingly ir- regular or crooked ; such are the vertebrce, or bones of the spine, and some of the bones of the face. These have a great many projections stand- ing out from them, to furnish more room for the attachment of muscles. The long ridge of bones which may be felt in the back, extending down- ward from the head, is composed of long projec- tions from the bodies of the vertebrae. These pro- jections are called the Spinous Processes,

Each of these forms of bone has its peculiar ad. vantages, and it will be found, on inspection, that the integral construction of each bone very greatly assists its general shape, in its applicability to its particular purpose in the skeleton. A few of these will be enumerated.

134

MOTORY APPARATUS.

128. 1st, The long bones. When one of these is sawn in two across the middle, it will be found to have a hole running longitudinally through it, the diameter of which is nearly one half of the whole diameter of the bone.

Fig. 43. This canal, during life, contains

a semifluid substance called mar- row, which has a double purpose ; it serves as a bed in which are placed the principal bloodvessels of the bone for their better protec- tion, and it answers for nutriment to supply the whole body when disease or privation overtakes it. There is here a reservoir of food always at hand, which, in time of health, is kept full, and readily ac- cessible when required to supply deficiencies from the usual sour- ces.

This cavity in the bone serves also an important mechanical pur- pose. By taking from the bone so much of its solid structure, it renders it also much less heavy, but without depriving it of any of its strength. On the contrary, it

Section of a Thigh -^ supposed that this cavity has the

Bone, showing the l l . u /^

canal, C, running ciiect of mcreasmg the firmness

through it. of the bone. The long bones be-

ing all levers, and having to bear the greatest bur- dens of the body, the strongest forpi, as well as the firmest material, must be employed. No form combining strength with lightness can be found

MOTORY AFPARATT7S. 135

more capable of sustaining a great strain or a heavy weight than that of the arch, and in the hollow cylindrical bone we have a double arch, A great point to be attained in the construction of such a bone is to arrange the least possible quan- tity of matter in the most advantageous manner.

To prove the superiority of this form, take half a sheet of letter paper, and roll it into a cylinder or tube about half an inch in diameter. If this tube is held firmly in the hand by one end, a con- siderable weight may be suspended upon the other end, by a string passing over it, without its bend- ing. If, then, the paper be flattened down so as entirely to destroy its arched or tubular form, it will not support by far so heavy a weight as be- fore, although the quantity of material is precise- ly the same. The form alone gives it greater strength. This simple but beautiful mechanism is applied with all its advantages to all the long bones of the body.

129. 2d, The flat bones. These bones, occu- pying very different situations in the skeleton, are variously constructed. The shoulder blades (which form the tops of the shoulders, and are plainly to be seen and felt on the back, each side of the spine), for their apparent size, are the light- est bones in the body. The principal part of them is devoted simply to the attachment of various mus- cles, without any particular requisition for strength, except at the upper end, where it forms a part of the shoulder joint, and is very strong. They hav3 so little substance in the broadest part of them as to be diaphanous.

The hip bones. These are much thicker than

M 2

136 MOTORY APPARATUS.

the last mentioned bones. When they are in

their proper places in the skeleton, they form the

basis on which the spinal column rests ; and they,

in turn, are supported by the lower extremities, as

in them are the sockets of the hip joints. In their

natural positions they are so situated with regard

to each other, as, together with the last bone of the

spine, to form a kind of basin ; hence this part of

the skeleton is called Pelvis.'^ By referring to the

front view of the skeleton, it will be seen that this

basin is placed, as it were, nearly on its edge, so

that the rim or edge of the circle is presented

nearly in a full view. By this arrangement, this

ring of bones is made to act in a double capacity.

1st, As a hasin to support the bowels, stomach, and

all the abdominal viscera ; and, 2d, As a double

arch, resting upon the thigh bones, and sustaining

the spine and all attached to it.

On examining these bones, they will be found to have several vacancies at dilTcrent parts ; for in- stance, in the lower front part is a large oval-shaped hole, and in several parts of the two edges are deep notches ; all of these, particularly the hole in the body of the bone, serve the very important purpose of diminishing the weight, which they do without lessening the strength of the part, but ra- ther increasing it, at the same time giving more points for the adhesion of muscles.

The other flat bones, viz., those of the head, present some very interesting and peculiar points, which will be noticed in another place.

130. 3d, The cubical and irregular bones are

♦ A Latin word, signifying a sort of vessel which was used in washing the feet.

MOTOR Y APPARATUS. 137

only remarkable as presenting a great variety of shapes, each being somewhat different from all the others, and curiously adapted to its place and uses. They will all be more particularly described un- der other heads.

THE JOINTS.

131. The means through which the muscles are enabled to act upon the skeleton, viz., the Joints, next claim our attention.

Whenever a motion is made between tw^o bones, however slight it may be, there is to be seen there an apparatus for facilitating the action. There is a certain arrangement of appropriate materials in the construction of the joints, contrived with great ingenuity, evincing a foreknowledge, an adaptation of means to ends, which precludes all possibility of admission to the thought that the animal machine merely Jiappened in its present state of perfection ; a construction which is in itself an argument alone sufficient to prove a Maker. In the construction of an engine of any kind, the mechanic, in making its moveable joints, aims at three principal points ; viz., sireiigtli in the formation, durability in the ma- terials, and freedom from friction in the working. The first point he gains by using some particular arrangement best adapted to the form of joint re- quired ; to procure a durable joint, one which will bear a great deal of working without wearing out, he generally constiTicts it of material much harder than the other parts of the machine. Thus, in a steam-engine, the parts which move upon each other are generally faced with steel ; and in a

138 MOTORY APPARATUS.

watch, very often, the pivots are made to run in sockets formed of precious stones, which are very hard. To diminish friction in large machines^ common oil is used to lubricate the joints and cause the parts to pass smoothly over each other ; but in more delicate constructions, as a watch, great pains must be taken to procure some lubricating material which will not become stiff and drv, oth- erwise, instead of assisting, it would interfere with and clog the movements of the apparatus.

Such a substance is a great desideratum, and, until lately, nothing has been known to answer all the required ends.

Nevertheless, with all the ability of human intel- lect, no machine has ever yet been made which would not wear out in some of its parts in a com- paratively short period ; either the material would give way, the moving power would be exhausted, the joints become stitf and immoveable, or the parts rubbing upon each other become worn off and re- quire renewal ; or the lubricating fluid would be- come deteriorated, or its supply cut off, and the ma- chine be obliged to stop for want of it. Neither, it may be said, was there ever an artificial machine in which the mechanic has not observed some de- fect which he might have avoided could he have foreseen it, or some part wherein an improved form is admissible.

If, then, man, with the wisdom of ages and all his boasted ingenuity, cannot produce a machine without such striking defects, and if we can point to a machine entirely free from all these objections and deficiencies, which can supply all its own wants ; one which we know man cannot make, and

MOTORY APPARATUS. 139

of which the first was as perfect as the last one made, shall it be said that that machine was made by chance ? that no thought was used in its con- struction ? To the mechanism of the joints of the animal body we can point in full confidence of their sufficiency to establish incontrovertible proof of the existence of an Architect infinitely surpass- ing man in ingenuity of design and power of ex- ecution.

132. A joint is the union of two bones with each other, and may be either moveable or immoveable. The latter kind are few in number, and will be no- ticed in another place. Of the moveable joints there are several varieties, as,

1st, The ball and socket joint.

2d, The hinge joint.

3d, The combination joint, being the ball and socket and hinge joint combined.

4th, The pivot or wheel joint.

5th, The sliding joint.

6th, The suture or immoveable joint.

Each of these kinds has its peculiar advantages, and even of the same kind there will be found some variations of form in different instances, to suit its position and requirements.

133. Of the ball and socket joint there are two examples in the shoulders and two in the hips. The latter form the most complete specimens of this variety of articulation. The principal superi- ority of this species of joint consists in the great latitude of motion which it admits of. It is formed by the end of a long bone being rounded into a large, smooth head or ball, which is inserted into a cavity or socket made in the opposite bone of the

140

MOTORY APPARATUS.

joint, and in which the ball revolves in every di- rection.

Fig. 44.

H ft, portion of the Hip bone, in which is excavated the socket, S, of the joint. T b, the Thigh bone. H, its head, the ball of the joint. N, the neck of the Thigh bone. P, a projec- tion for the attachment of powerful muscles.

134. In the hip joint, the cavity forming the socket is made directly in the body or substance of tiie hip bone, and its c(\^ is sligiitly raised above the plane of the bone. But this depression

WOTORY APPARATtlS. 141

in the bone is not by any means deep enough to keep the ball in its place ; its depth is, therefore, very much increased by a border of cartilage (which is next to bone in hardness), which is raised about half an inch, and inclines a little inward, so as to embrace the head of the thigh bone. It will be perceived, that the greater the depth of the socket, the less freedom of motion must there be to the thigh bone, but the greater must be the se- curity against dislocation. If the socket were made more shallow, the joint might have had a freedom of motion incompatible with its safety ; even as it is, the ball is forced out of its socket fre- quently by violent twistings of the limb.

135. But this raised edge of the cartilage alone would not have been a sufficient protection against its displacement ; and we find it most happily fur- nished with other preventives against such a sad accident. These consist of a peculiar substance called Ligament, which has the strength nearly of tendon, and is equally pliable. There are two lig. aments in the hip joint very different from each other in form. Both may be seen represented in fig. 45. One is in the form of a short cord, and lies within the joint, passing from the head of the thigh bone to the centre of the socket, connecting them together ; and being very firmly fastened to the bony substance at each end, it serves to keep the ball from slipping from the socket, unless force is applied sufficient to break it. It is long enough to allow the greatest extent of motion requisite to the joint, and not so long but that it will keep the ball within its proper limits. From its form it is called the Round Ligament

142

MOTORY APPARATUS.

Fig. 45.

R L, the Round Ligament. C L, the Capsular Ligament^ cut open to show the interior of the joint.

136. The other Hgament is, from its shape, being that of a bag or cap, called the Capsular Ligament. This is situated outside the joint, and surrounds it completely, so as to conceal it from view. If the reader will suppose the ball of the joint to be in its place in the socket, and then a broad band to be wound once around the two, so as entirely to em- brace them, and fastened to each by its edges, he will have a good idea of the situation of the capsu- lar ligament. In fig. 45, part of this ligament may be seen. It is, in fact, a cylinder in shape, of which one end is attached to the circumference of the socket, and the other encloses the ball. This ligament is quite loose around the joint, so that it does not interfere with its motions ; it exerts also

MOTORY APPARATUS. 143

some power in preventing dislocation ; but when this accident does occur, it is ruptured by the head of the thigh bone being forced through it. One of the most important uses, however, of this Hga. ment, is to retain within the joint the lubricating fluid, some of which might otherwise escape.

THE MEANS TO PREVENT WEAR AND FRICTION.

137. It will be obvious to all who examine this structure, that if the bare surface of the ball were presented to the like surface of the socket, that is, if the two bony surfaces were allowed to rub against each other, it would take but a little while, with the almost incessant action of this joint, to wear them both away so as to be useless, and require a long time to renovate them. .The manner in which such a result is guarded against, is simple and effectual, as well in giving smoothness to the rubbing surface, as affording protection to the bones. Each opposing part is covered with a coating of cartilage^ whose endowments of elasti- city and glairy smoothness afford surfaces the most complete imaginable for all the purposes of a joint. Were it the case even that no means had been given to increase their natural smoothness of surface, the cartilaginous faces of the joint would have been almost sufficient of themselves to pre- vent injurious friction ; but, as if nothing short of absolute perfection would satisfy the Great Ar. chitect, there is added to this mechanism a little ap- paratus for furnishing a lubricating fluid, which re- moves every possible chance of friction. Im- mediately between the ball and socket of the joint

N

144 MOTORY APPARATUS.

lies a little sac which has no opening, denomina- ted anatomically a shut sac. This sac is large enough to cover the head of the thigh bone, one side of it lying in contact with its surface, and the other side of the sac being adapted to the surface of the capsular ligament, and, in fact, every part of the internal surface of the joint is closely lined with it. It therefore partakes in every movement of the parts. Upon its internal surface is exuded the lu- bricating material, which is called Synovia, It re- sembles a thin jelly in consistence, and has an in- comparable slipperincss and unctuous feel ; and always existing, in a healthy state, in sufficient quantities, and being continually renewed as it is exhausted by use, the articulating apparatus is thus kept in a pliant condition, ready, at the bidding of a thought, to operate with perfect smoothness, and with the least possible degree of obstruction from friction.

138. Another source of strength to the joint, and as effectual a one, is the muscles which lie around and cover it to the depth of several inches, and which are the means of its motion. These mus- cles are the most powerful in the