Elements of animal physiology, chiefly human : with hints on practical work, dissection, &c

Front matter

William Collins, Sons, & Co.’s Educational Works.

COLLINS’ ELEMENTARY AND ADVANCED SCIENCE SERIES,

Adapted to the requirements of the South Kensington Syllabus,, for Students in Science and Art Classes, and Higher and Middle Class Schools.

Preface

Animal Physiology is “ essentially a Science of Designs and Final Causes.” Probably no subject, if taught with even moderate intelligence, can be rendered so interesting, or made to rouse the dormant energies of the intellect of young people, and of those previously untrained in the method of scientific inquiry, as that of Human Physiology ; Certainly the study of no other science opens up to the mind so many wonders, solves so many human mysteries, or brings home to the mind so many proofs of the “reign of Law,” and of the wise and beneficent design of this universe, or teaches so many principles which lie at the basis of human health, morals, and wellbeing, as that of Human Physiology. On these considerations alone, — and many other most powerful ones might be urged, — “ Human Physiology” must claim a leading position in any system which professes to educate the people soundly.

~ Very considerable experience as a Teacher of Physiology, with the youthful and adult of both sexes, has proved to the writer the facility with which the viva voce teaching of Elementary Physiology may be made “ perfectly sound and thorough,” when supplemented with the aid of good diagrams, a good text-book, and the free use of the black-board, and of the lungs, heart, kidney, eye, &c., of the sheep, and of such other objects as may be readily obtained from the butcher, for the illustration of the general structure of the corresponding organs of the human body ; while the body of the living frog or tadpole is amply sufficient to illustrate the general phenomena of tne circulation and the properties of the living tissues. The teacher should also occasionally dissect a small animal, as a rabbit, recently killed with chloroform, before his class. Human Skeleton and a cheap Microscope will likewise be found invaluable aids to the earnest teacher.

A o-eneral impression prevails, among the candidates presenting themselves at the Government Science Examinations, that it is easier to pass with the same actual knowledge m the Second Class, Advanced Stage, than in the First Class, Elementary Stage. The prevalence of this error can only have resulted from the candidates having confined tiieir iv

PREFACE.

attention too exclusively to the subjects named in the Syllabus of the Elementary Stage, whereas it is impossible to obtain a sound , however elementary, knowledge of these subjects themselves, without their also making themselves familiar, as it were, with the atmosphere of facts immediately surrounding them. To obviate this difficulty, promote greater soundness of attainment, and especially with the object of cultivating the higher reasoning powers of the young student in dealing with the principles of the science, rather than encourage in him the acquisition of the power of what may be expressed as mere “descriptive cram,” the writer has dealt, as at the opening of the book, and in treating of the blood and the tissues, far more with the principles and the reasoning of the subject than is usual in treatises of the same limited and elementary character. He has therefore been compelled to extend the range of this little work beyond the subjects actually named in the Syllabus of the Elementary stage issued by the Department of Science and Art. He has also everywhere sought, — as by sectionizing the work, by making it as practical as possible, by the mode of keying the diagrams, &c., — to make it as clear and thorough as his limits would permit, never hesitating to repeat, where he felt repetition would be advantageous to the student.

The writer begs, in conclusion, to express his indebtedness to the works of Bennett, Carpenter, Combe, Gray, Lawson, Marshall, Playfair, Huxley, and others; to the latter especially for kindly allowing him to copy some of the diagrams in his text-book on the same subject. To Professor Huxley all friends of the cause of scientific education are, in common with the writer, indebted, not only for his labours as an Englishman in extendiug the domains of Biological Science, but also for his able and successful advocacy of the claims of “ Physiology ” as a branch of general popular education.

John Angell.

Manchester, August, 1873.

CHAPTER I. General View of the Scheme and Functions of

the Human Body.

The Living Body compared with a Steam Engine at Work, 1— Physiology and Theology in Harmony, 2-3— Comparison of the Actions of a Living Body with those of a Steam Engine, continued, 4-6— Helmholtz’s Estimate of Total Internal and External Mechanical Work of Living Man per day, 7-9— Dr. Frankland’s Estimate of Mechanical equivalent of 20| ounces of Oatmeal, 10— Difference between Living Body and Working Steam Engine, 12-13— Living Body Self -Repairing, 14-15— Change and Waste, 16— Proof of Development of Heat Force in the Living Body, 17-18— Of Mechanical Force, 19-20 — Of Vital and Nervous Force, 21 — Waste Processes, 22 — Proofs of Waste, 23 — Waste Increases with Work, 24 — Diurnal Balance, 25 — Hunger and Thirst, 26 —Ingestion of Oxygen a Condition of Life, 27-28 — Death, 29 — Reproduction, 30 — The Cognate Sciences, 31, ..... Pages 9-22

CHAPTER II. General Build of the Human Body

Divisions of the Human Body, 32— Head, 33— Trunk, 34— Thorax, 35-36 — Cavity of Abdomen, 37 — Hints for Lay Students, 38 — The Extremities, 39-41 — Transverse Section of a Limb, 42— Investing Membranes, 43 — Blood-vessels, Nerves, and Absorbents, 44 — Double tube theory of Structure of Animal Body, 45— Typical Vertebra, 46-47, ....... Pages 22-31

CHAPTER IV. Chemical Preliminaries

Analysis of Human Body, 88 — A Chemical or Ultimate Element, 89 — The Organogens, 90 — Oxygen, 91 — Hydrogen, 92 — Water, 93 — Nitrogen, 94 — Ammonia, 95 — Atmospheric Air, 96 — Carbon, 97 — Carbonic AcidGas, 98 — Putrefaction, Decomposition, and Decay, 99- 100 — Incidental Elements, 101 — Mineral Compounds, 102 — Endosmosis, &c., 103 — Diffusion of Liquids and Gases, 104 — A Proximate Principle, 105 — Albumen, 106— Fibrin, 107 — Syntonin, 108 — Casein, 109 — Globulin, 110 — Gelatin, 111 — Chondrin, 112 — Keratin, 113 — Protoplasm (bioplasm), 114 — Non-nitrogenous Principles, 115 — The Amyloids, 116 — Starch, 117 — Dextrine and Gum, 118 — Sugar, 119 — Fats, 120 — Organ and Organized Bodies, 121 — Function, 122 — Biology, 123 — Anatomy, 124 — Physiology and Pathology, 125— Histology, 126, ...... Pages 47-59

CHAPTER V. Histological Preliminaries

Epithelium, 127-131— Connective, Cellular, or Areolar Tissue, 132 — White Fibrous Tissue, 133 — Yellow Fibrous Tissue, 134— Adiposo

VI

CONTENTS.

Tissue, 135 — Cartilage or Gristle, 136 — Osseous Tissue, 137 — Enamel, 138 — Dentine or Tooth Tissue, 139 — Crusta Petrosa, 140 — Muscular Fibre, 141-144 — Nervous Tissue, 145-151, . . Pages 59-74

CHAPTER VI. The Blood

The Blood, 152 — Appearance and Properties of, 153 — Magnified Blood, 154 — Structural Character of, 155 — General Composition of, 156 — The Red Corpuscles, 157-158 — Form and Size of Red Corpuscles in various animals, 159 — Structure of Red Corpuscle, 160-161 — Cause of Colour of Red Corpuscle, 162 — Detection of Blood Stains, 163 — Function of Red Corpuscle, 164 — The Oxygen in Feeble Chemical Union with the Blood, 165 — Transfusion, 166 — White Corpuscles, 167-170 — Liquor Sanguinis, 171-72 — Coagulation of Blood, 173-175 — Serum, 176 — Serosity of Blood, 177 — Magnified Coagulated Blood, 178-179 — Cause of Coagulation, 180-182 — Wounds after Death, 183 — Conditions which Accelerate or Retard Coagulation, 184 — Buffy Coat, 185 — Cupped Appearance of Blood, 186 — Gases in Blood, 187 — Functions of Blood, 1SS— Gains and Losses of, 189, Pages 74-90

CHAPTER VII. Cumulation of the Blood— The Heart and Blood-vessels

General Purpose of the Circulation, 190 — Description of, 191 — Position and Size of the Heart, 192 — Structure of, 193— The Auricles, 194- 195 — Ventricles, 196-197 — Chordae Tendinese, 198 — Movements of Heart, 199- -Beating of, 200 — Course of Blood through, 201-202 — Valves of the Heart, 203-207 — Pericardium, 208 — Endocardium, 209 — Sounds of Heart, 210 — Arterial Pulse, 211-212 — Nerves of the Heart, 213 — Arteries, 214-216 — Aorta, 217— Cceliac Axis, 218 — Structure of Arteries, 219-224— Vaso-Motor Nerves, 225— Capillaries, 226 — Veins, 227-228 — The Valves of, 229 — Venous Pulse, 230 — The Vasa Vasorum, 231 — Blushing, 232-233 — Cause of Congestion, Cholera, &c. , 234— Pallor, 235— Evidence of Circulation in Living Body, 236, ..... Pages 91-115

CHAPTER VIII. Respiration— The Lungs

Part played by Oxygen in the Animal Economy, 237 — Respiration, Definition of, 238— Changes in the Blood during Respiration, 239 — Proofs of Waste through the Lungs, 240 — Scheme of Structure of Lungs, 241-242 — Pressure of Air in, 243— Course of the Air in Breathing, 244 —The Air-tubes of the Lungs, 245-249 — Infundibula, 250 — Air Cells, 251 — Cilia and Ciliated Epithelium, 252 — Blood-vessels of Lungs, 253 — Composition of Air, 254— Changes in Respired Air, 255 — Ventilation, 256 — Source of the Carbonic Acid, 257 — Mechanical Movements of Respiration, 258 — The Thorax, 259 — Pleura, 260 — Diaphragm or Midriff, 261 — Ordinary and Extraordinary Inspiration, 262-263— Ordinary and Extraordinary Expiration, 264-265 — Costal or Pectoral Respiration, 266 — Diaphragmatic or Abdominal, 267 — Snoring, 268 — Sighing, 269— Sniffing, 270 — Yawning, 271— Coughing, 272 — Sneezing, 273 — Sobbing, 274 — Hiccough, 275— Crying and Laughing, 276- — Frequency of Respiration, 277 — Residual, Tidal or Breathing, Complemental, and Supplemental Air, 278-281 — Capacity of Lungs, 282 — Artificial Respiration, 283 — Asphyxia (suffocation), 284-285— Respiratory Sounds, 286,

CONTENTS.

Vll

CHAPTER IX. Animal Heat

Animal Heat, 2S7 — Effect of Exercise on and Amount of, 288— Regulation of, 289— Average Temperature, 290— Warm and Cold-Blooded Animals, 291, ..... Pages 136-137

CHAPTER X. Digestion— Organs op Digestion

Digestion, Definition of, 292— General View of the Alimentary Canal, 293 — General View of the Course of the Food and its Changes, 294- 295 — The Mouth, 296-297 — Mastication or Chewing, 298 — The Teeth, 299 — Structure of, 300 — Permanent and Milk Teeth (incisors, bicuspids, molars), 301 — Insalivation, 302 — Salivary Glands, 303 — Saliva, 304 — The Pharynx, 305— (Esophagus, 306— Deglutition (swallowing), 307-311 — Drinking, 312 — The Stomach, 313-316 — Gastric follicles or Tubuli, 317 — Gastric Juice, 318 — Chymification (gastric digestion), 319 — Chyme, 320 — Artificial Digestion, 321 — The Pylorus, 322 — Large and Small Intestines, 323 — Intestinal Digestion (chylification), 324 — The Duodenum, 325 — Jejunum, 326 — Ileum, 327 — Peritoneum, 328 — Mesentery, 329 — Caecum, 330 — Colon, 331 — Rectum, 332 — Intestinal Villi, 333, . . Pages 137-155

CHAPTER XI. Food and Nutrition

Food, Definition of, 334 — Classification of, 335-336 — Digestibility of, 337 — Relation of to Daily Loss, 338 — Economical Admixture of, 339 — Nutrition, 340, .... Pages 155-159

CHAPTER XII. The Lymphatics, Lacteals, and Thoracic Duct

The Lymphatic or Absorbent System, 341 — Thoracic Duct, 342 — Receptaculum Cliyli, 343— Lacteals, 344— Lymphatics, 345— Lymphatic Glands, 346— Mesenteric Glands, 347 — The Lymph, 348— Chyle, 349, ...... Pages 159-162

CHAPTER XIII. Secretion and Excretion— Structure op Glands

Secretion, Definition of, 350 — Excretion, 351 — A Gland, 352— Plan of Structure of Glands, 353-356 — Classification of Glands, 357 — Tubuli of, 358— Glandular Epithelium, 359— Glandular Ducts, 360-361— Vital Selective Force of, 362— Theory of Secretion, 363— The Liver, 364-368— The Ducts of, 369-372— Gall Bladder, 373— Portal Vein, 374 — Hepatic Veins, 375 — Hepatic Artery, 376 — The Bile, 377 Glycogen, 378— Proof of Glycogenic Function of Liver, 379— Glucose, 380— Nerves of Liver, 381— Pancreas, 382— Pancreatic Duct, 383— Pancreatic Juice, 384— Salivary Glands, 385, Pages 162-173

CHAPTER XVII. Animal Mechanics— The Muscles, Tendons, Joints, Ligaments, and Levees

Animal Mechanics, 413 — The Muscles, 414-417 — Tendons or Sinews, 418 — Ligaments, 419— The Articular Cartilages, 420 — Synovial Sacs, 421 — The Joints, 422-428 — Supination, 429— Pronation, 430 — Levers, 431-435 — The Erect Position of the Body in Standing, 436 — Walking, 437 — Running, 438 — Jumping, 439, . . Pages 187-195

CHAPTER XVIII. The Organs op the Voice

The Voice, 440-441 — Speech, 443 — The Larynx, 443-449 — The Vocal Chords, 450-452 — Pitch or Note, 453 — Loudness of Voice, 454- Essentials to the Production of Voice, 455 — Vowel Sounds, 456 — Consonantal Sounds, 457, .... Pages 195-201

CHAPTER XIX. — The Senses and the Organs op the Senses

The Organs of the Senses, 458-459 — Muscular Sense, 460 — Touch, 461-462 — The Tongue and Taste, 463 — Smell, 464 — The Nose, 465 — Sound, 466 — Hearing, 467-468 — The Vestibule, 469 — Semicircular Canals, 470 — Membranous Labyrinth, 471 — Otoconia, 472 — Function of Labyrinth, 473 — The Cochlea, 474-475 — The Modus Operandi of Hearing, 476 — Light, 477 — Undulatory Theory of Light and Colour, 478-479— Complementary Colours, 480 — Colour Blindness, 481— The Eye, 482-483 — The Sclerotic Coat, 484 — Cornea, 485 — Choroid Coat, 486 — Iris, 487 — Aqueous Humour, 488 — Crystalline Lens and Long and Short Sight, 489 — Vitreous Humour, 490 — The Retina, 491-492 — The Blind Spot, 493-494 — Bright Spot of Sommering, 495 — Duration of the Impression of Light, 496— Erect Vision, 497 — Single Vision with two Eyes, 498 — Double Vision with one Eye, 499 — A Phosphene, 500 — Purkinje’s Figures, 501 — The Adjustment of the Eye, 502 — The Ciliary Muscle, 503— Muscles of the Eyeball, 504 — Appendages of the Eye, 505 — Eyebrows, 506 — Eyelids, 507 — Conjunctiva, 508 — Lachrymal Glands, 509, Pages 202-222

CHAPTER XX. The Nervous System. Innervation

The Nervous System, 510-511 — Innervation, 512 — Sensation, 513 — The Brain, 514 — The Cerebrum and its Function, 515-516 — The Cerebellum, 517 — The Pons Varolli, 518 — The Cranial (cerebral) Nerves, 519 — Medulla Oblongata, 520-522 — The Spinal Cord, 523-528 — The Membranes of, 529 — Functions of, 530 — Reflex Action, 531 — The Spinal Nerves, 532 — Injury or Irritation of, 533 — The Sympathetic Nerve System, 534-535, .... Pages 222-232

Appendix. — Hints for the Dissection of a Rabbit, Ox’s Eye, and Sheep’s Brain; Extra Diagram of Thorax, and Government Science

Questions,

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Index, , » .

ANIMAL PHYSIOLOGY.

Chapter I. General View Of The Scheme And Functions Of The Human Body

1. The Living’ Body compared with a Steam Engine at Work. — The body of a living man in many respects closely resembles that of a steam engine at work, differing from it chiefly in the greater variety, complexity, beauty, and perfection of its individual parts, and its scheme as a whole, just as its contriver and maker, man, differs in power and degree from the great Maker of the Universe.

2. Physiology and Theology in Harmony. — At the outset, to prevent all possible confusion, let it be distinctly understood that, though we shall frequently have cause to refer to the nature and the condition of the action of the human mind, we in no case intend, as not coming within the proper province of “ physiology,” to refer to the nature of the human sold, or its connections or relations with the human body.

In the opinion of the writer, as far as mere human knowledge and intellect are concerned, the nature of this connection is entirely a mystery : all attempts to investigate this divine, not human, problem have hitherto not only failed to present any light on the wonderful mystery, but have entirely failed even to show us how, by any scientific ov jihilosophical methods with which we are acquainted, we shall be able to acquire such knowledge.

In fact, we at the present time are not only without

ANIMAL PHYSIOLOGY.

such knowledge, in the sense in which the term is used in science, but are also utterly helpless as to the method by which such knowledge is to be 'philosophically acquired or built up. The writer of this little treatise would even go so far as to express it to be his opinion that the Almighty, in creating man, withheld from him, as he has also withheld from him the power of prophecy and other Divine gifts, the faculty of acquiring during this life any true knoAvledge of the nature of the human soul.

3. Some writers, it is true, have endeavoured to support, on the basis of physiological argument, the theory of the utter extinction and annihilation of man by death. With this view the writer of this little book has no sympathy whatever. In any case the proposition, being incapable of scientific proof, must remain in the region of pure hypothesis. To the present writer the fact that the Great Creator of all things has endowed man, as a part of his nature and his mental being, with the fundamental faculty or the natural sentiment of religion, in consequence of which mankind, even in the absence of true knowledge, has at all times and during all ages practised religion, true or false — has at all times cultivated a belief in an existence future to death — seems (to the writer) distinctly to point to, and make as eminently reasonable, the belief in the truth of the future existence or the immortality of man, as the structure of the heart and great blood-vessels, and the arrangement of the valves, rendered reasonable to the great physiologist (Harvey) the fact of the circulation of the blood.

In any case, the fact that the theory of our “ future life ” is compatible with all the promptings of our religious, moral, imaginative and poetical faculties, that it cannot but tend to elevate and purify our lives, and render them less selfish, is a sufficiently reasonable and practical argument, in the absence of all scientific proof to the contrary, why this theory, coinciding as it does with the doctrines of Christian Revelation, should be adopted as the basis of our practical rule of life. Be this,

ACTIONS OF A LIVING BODY WITH A STEAM ENGINE. 11

however, as it may, the writer having frankly, and ho trusts respectfully, expressed his opinions on the subject of the “ future existence of man,” hopes that he will not be deemed responsible for the action of those who, with a very limited knowledge of “ physiology,” and a still more limited knowledge of things in general, may attempt to extort , or rather distort, from statements in this little work arguments subversive of this theory, or of the belief in the existence of the human soul.

4. Comparison of the Actions of a Living Body with those of a Steam Engine continued. — What, then, is a steam engine 1 and in what respects, it may be asked, can two such apparently dissimilar objects as a steam engine and the body of a living man resemble each other?

A steam engine is a complex structure, by means of which —

1st. Chemical force, stored up in certain materials (the fuel), is converted into heat force.

2nd. Heat force is converted into mechanical force.

3rd. The mechanical force is made to do the work desired by the designer and constructor of the engine.

The real force which drives the steam engine is not the steam, but the heat. The steam is merely the medium or agent by means of which the heat- is most conveniently brought to bear upon the solid parts of its machinery.

5. For the construction of a steam engine we require —

(1.) A grate or furnace, in which the f uel is burnt or

Oxidized — that is, made to combine with the oxygen of the air, so that its chemical force may be converted into heat force. The grate or furnace corresponds to the lungs and capillaries.

(2.) A boiler containing water, placed where it shall receive the utmost possible heat from the combustion taking place in the furnace. All heat which does not pass into the water in the boiler is so much lost force, and the fuel consumed in generating it is so much lost fuel.

(3.) A cylinder, piston, and piston-rod, which correspond

ANIMAL PIIYSIOLOGf.

in function with those of the bones, ligaments, musclest and tendons of the living body.

The cylinder is a large hollow cylindrical vessel connected with the boiler by a steam pipe.

The piston is a circular flat disc of metal, fitting air-tight into, and capable of being pushed up and down, the cylinder.

The piston-rod is a strong metallic rod attached to the ripper or outer part of the piston.

When the water in the boiler has received the necessai’y quantity of heat, it expands with enormous force to neai’ly 1,700 times its original bulk or volume. The capacity of the boiler being fixed and limited, it is unable to contain this additional bulk or volume of expanded water (steam) which thus forces its way, or rather is driven by the heat into the cylinder , pushing the piston and piston-rod before it, thus producing the available mechanical force for the development of which the steam engine has been set up.

(4.) The steam governor, which is a mechanical arrangement by which the quantity of working steam — that is, the quantity of steam delivered into the cylinder — is regulated according to the resistance of the engine or the roork to be done. That is, if more power is required because more work is to be done, then more ivorking steam is admitted to drive the piston in the cylinder. If work is taken off so that less work is to be done, less working steam is admitted, — the fuel consumed being regulated accordingly by the man in charge of the engine.

The steam governor of the steam engine, together with the stoker or man who attends to the furnace, corresponds to the sympathetic or organic nervous system of the living man, which regulates or duly adjusts the action of the digestive, respiratory , circulatory, and muscular systems with regard to each other; so that in health they should not work too fast or too slow for each other — that is, that the organs of digestion should not make too much or

too little blood, or the heart drive it too slowly or too

ACTIONS OF A LIVING BODY WITH A STEAM ENGINE. 13 rapidly through the system, or the lungs oxidize it too highly or too feebly, or the tissues appropriate it too quickly.

(5.) Various mechanical contrivances, not here necessary to describe, by means of which the mechanical force , originating as previously explained in the first instance out of the heat, is distributed and directed so as to accomplish the various ends for which the engine was designed. These parts also, like the piston, piston-rod, <fcc., thus used for transmitting and directing mechanical force and movement, may also be compared with the bones, muscles, ligaments, and tendons of the living body.

6. The amount of work expressed in mechanical units done by a well constructed and well managed steam engine (allowing for loss by friction, &c.) is in the ratio of the fuel consumed. That is, roughly speaking, for twice the fuel consumed, twice the mechanical power, should be developed, and twice the work be capable of being done.

7. According to Helmholtz, the celebrated German physicist, the total internal mechanical work of a living man is not less than about 715,000 foot pounds per day, of which 500,500 foot pounds are expended in the mechanical work of the circulation, 78,650 foot pounds in carrying on the mechanical work of respiration, and 135,850 foot pounds in the performance of the mechanical work of other internal processes of the living body.

8. Helmholtz also estimates the external work — that is, the external resistance overcome by an active, vigorous working man per day — at about 715,000 foot pounds.

9. Every 2£ lbs. of good coal burnt in feeding a good steam engine should be capable of producing about 2,145,000 foot pounds of mechanical force; thus the mechanical work producible by the combustion of one kilogi’amme, or about 2-J lbs. of coal, equals the mechanical work of three men for a whole day.

10. Dr. Frankland has estimated that 20^ ounces of oatmeal (at a cost of 3^- pence), oxidized in the body of a small living man (weighing 140 lbs.), would enable him

ANIMAL PHYSIOLOGY.

to raise himself 10,000 feet high (as in ascending a mountain) ; or, in other words, would enable him to expend 1,400,000 foot pounds of mechanical force.

11. The steam engine is thus an instrument by which heat and mechanical force are developed out of the chemical force stored up in the fuel consumed in working it.

12. Difference between the Living Body and a Working Steam Engine. — The living human tody is, however, a far higher and more complex structure, in which a cei’tain amount of chemical material (the food) is daily consumed and' oxidized , the chemical force evolved during the combustion of which is not simply converted into the ordinary forms of heat and mechanical (muscular) force, but also into the various forms of nervous, vital, and mental force.

13. In the living body, as in the case of the steam engine, the quantity of force developed depends on the quantity of food profitably consumed (that is digested, assimilated, and oxidized). Where more food is consumed more force is developed. And where more work, either brain or muscular, is to be done, more food must be consumed to supply the requisite force.

14. The Living Body Self-Renewing and Self-Repairing. But the living human body, viewed as a mere machine, differs from that of a steam engine, not merely in the greater number and higher nature of the forces developed by the oxidization of its food and tissues, but also in its self-reparative and its reproductive power.

The steam engine works and wastes or wears itself away, and, therefore, soon requires repair from external sources, or mending by external agents.

The living human body, on the contrary, requires no such external aid, but during health is seZ/’-reparative, constantly wasting away, constantly expending both force and substance, yet neither losing power nor weight, that is, preserves from day to day its average weight and strength.

15. This power of self-repair is characteristic only of animate beings. No construction of man, however in-

HEAT FORCE IN THE LIVING BODY. 15

genious, lias ever possessed this property. No man has yet designed , much less constructed , a clock or other instrument which though always at work, yet should never wear out, or which should repair itself or renew its parts as rapidly as they wear away; yet this is what occurs in all cases of healthy animal life.

16. Change and Waste. The living body is the seat of actions far more numerous and incessant than those of any mere inanimate object however complex.

Even during sleep, chemical, vital , nervous and mechanical movements are continually proceeding. The blood is ever circulating, the heart ever heating, the arteries ever pulsating, the chest ever throbbing, the oxygen of the air “ the sweeper of the living organism, but the lord of the dead body,” as it has eloquently been described by Professor Huxley, is ever combining with and destroying the tissues of the body. In fact, during life there is continuous action with its corollary — constant waste.

The explanation of the nature and extent to which these processes of continual change and waste are carried on in the living body forms one of the leading objects of the science of “ Animal Physiology.”

17. Proof of the development of Heat Force in the living body. Every boy who has played at snow-ball knows that, if he grasp a piece of ice or a small quantity of snow at freezing temperature ('0° Centigrade) in the palm of his hand, it will speedily melt. He also knows that the heat — the force by which this effect of liquifaction is produced — is derived from the body. Heat, therefore, is normally developed in the living body.

What takes place with respect to ice held in the hand, would take place with regard to ice placed in contact with any other part of the living body. Supposing the entire body to be encased in ice at freezing point (0° Centigrade), and the melted ice (the liquid) to be carefully and accurately weighed, the quantity of heat given out from the surface of the body might be ascertained with

ANIMAL PHYSIOLOGY.

great precision. Physicists thus ascertain by a process of calorimetry the quantity of heat contained in a body of given weight and temperature.

18. But, in addition to the heat given off from the surface of the body, a large quantity of the heat developed in the living body is also carried off by the breath, which as all know is considerably warmer than the air of cold or temperate climates. A knowledge of the origin of “Animal heat," and the conditions under which it is developed and distributed through the system, is also included in the science of Animal Physiology, which thus includes an elementary knowledge of chemistry, and of “heat,” as a branch of “Physics.”

The principal organs concerned in the development and regulation of the animal heat are the lungs, capillaries, and the shin.

19. Proof of the development of Mechanical Force in the living body. Throw a stone up through the air by means of the hand and arm. The movement of the stone is a mechanical movement, and the mechanical force by which it is effected is developed within the living body. At every step we take in walking, we raise the whole weight of the body ; every time we raise a limb or lift a weight, we generate and expend mechanical force. Mechanical force must therefore be abundantly developed in the bodies of living men.

20. The development and 'direction of the mechanical force generated by living beings is effected, as previously stated, mainly by organs termed respectively muscles, tendons, bones and ligaments. The branch of Physiology which specially treats on this subject is termed “Animal Mechanics.”