CHAPTER XVI

VOICE AND SPEECH

A cut carried horizontally backwards across the cartilage which projects forwards as Adam’s apple, a quarter of an inch below its notch, would show that it is =V=-shaped, the point of the =V= in front. Each limb of the =V= is a broad plate. In the mid-line is a gap, the rima glottidis, through which the windpipe communicates with the pharynx (Fig. 45). It is overhung by the stiff leaf-shaped epiglottis, the edge of which can be felt with the finger behind the tongue. (γλωττίς, the mouthpiece of a reed-pipe, is the term commonly used, for short, for the rima glottidis.) When air is being drawn into the lungs, the glottis is widely open. In speaking or singing it is almost closed. It is tightly shut whilst food is passing down the gullet.

The glottis is bounded, as to its anterior two-thirds, by two membranous folds, the vocal cords. In its posterior third it has a triangular cartilage, the arytenoid, on either side. A distinction is sometimes drawn between the anterior part, bounded by the vocal cords, and the whole glottis, the former being termed “rima vocalis”; but it is scarcely justified, for, although it is true that the anterior part is essentially the organ of voice, and its margins alone vibrate when high notes are sung, the anterior ends of the arytenoid cartilages also vibrate during the production of low notes. (The substance of these processes is not, properly speaking, cartilage; it resembles the epiglottis in containing a great abundance of elastic fibres.) And here we must warn the reader not to picture to himself a vocal “cord” as a kind of fiddle-string. It bears no resemblance to a cord, as we ordinarily understand the word; it is but a fold of mucous membrane, such as one might pinch up between finger and thumb from the inner side of the cheek. Its capacity for vibration depends upon the tenseness which is given to it by the pressure of the lymph with which it is distended, and vast numbers of exceedingly slender elastic fibres which traverse it.

The first cartilage below the thyroid—it may be felt with the finger—is termed “cricoid” (κρίκος, a ring), from its resemblance to a signet-ring. Narrow in front, its large signet projects upwards, within the =V= of the thyroid, behind, and on the top of the signet rest the two arytenoids. Each arytenoid is a triangular pyramid, its anterior, external, and upper angles prolonged into processes. It is united with the cricoid by a swivel joint, which allows its anterior process to swing inwards or outwards under the influence of two antagonistic muscles attached to its outer angle—the lateral and posterior crico-arytenoids. Another muscle attached only to the arytenoids draws them together. Still another muscle—or two muscles, for it is in two separate bands—unites the anterior process of the arytenoid with the back surface of the thyroid just on the outer side of the attachment into that cartilage of the vocal cord. The internal thyro-arytenoid muscle is a comparatively narrow band; the external thyro-arytenoid muscle is thick and broad.[3] By the simultaneous contraction of the encircling muscles the larynx is closely squeezed together, the anterior portion of the slit forming a =T=, with the transverse limb in front. This occurs only in swallowing. Under the co-operating contractions of the several muscles, the glottis assumes a variety of shapes. The external crico-arytenoids rotate the anterior angles of the arytenoid cartilages inwards (Fig. 45, A). If at the same time the arytenoid muscle draws the cartilages together, the glottis is reduced to a slit (Fig. 45, C). The posterior crico-arytenoid muscles rotate the cartilages outwards. If the arytenoid muscle is at the same time relaxed, the glottis gapes to its fullest extent (Fig. 45, A). The freer the opening, the less is the resistance to the blast of air, the gentler the vibrations of the cords, the lower the voice. The closer the slit, the greater is the resistance which the air in the windpipe has to overcome in passing through it, and consequently the more ample the vibrations into which it throws the vocal cords.

The vocal cords are the tongues of a reed-pipe, which, commencing in the chest at the point where the great bronchi join to form the windpipe, comprises the larynx, and, above the larynx, the complicated chambers of the throat, mouth, and nasal cavities, including the spaces within the bones of the head which open out of them. The pitch of the voice depends upon (1) the length of the vocal cords, and (2) their tension. The first factor is fixed for every individual. The voice is base, baritone, tenor, in a man; contralto, mezzo-soprano, soprano, in a woman—in proportion as the cords are long, of medium length, or short. A man’s vocal cords measure, on the average, 15 millimetres, a woman’s 11 millimetres. When a boy is from twelve to fifteen years of age his vocal cords double in length, and the “breaking” of the voice occurs as he gives up trying to get high notes out of his longer cords, and allows them to produce manly tones of an octave lower.

The lower posterior angles of the thyroid cartilages articulate with the cricoid. If the four cartilages are freed from all soft tissues without disturbing the thyro-cricoid, or crico-arytenoid joints, and if, while the thyroid is held in one hand, a finger of the other is placed on the front of the cricoid, it will be found that as this is depressed the arytenoid cartilages which rest upon its signet are tilted upwards and forwards within the thyroid; as it is raised, they are tilted away from it. In life this movement is effected by a muscle—the crico-thyroid (Fig. 46)—attached to the front of the cricoid cartilage and to the under border of the lateral plate of the thyroid. This is the muscle of supreme importance in the production of the voice. The thyroid cartilage is slung in a fixed position by the hyoid bone (to be felt in the neck above it). The crico-thyroid muscle, being unable to depress the thyroid, raises the front of the cricoid cartilage, tilts back the arytenoids, tightens the vocal cords. As the voice ascends the scale, the tension of the cords is progressively increased, and their vibrations rendered proportionately more rapid. The range of the human voice is about three and a half octaves; of individual voices about two octaves; if the shrill cry of a baby, which may reach the third G above the middle C, or even higher (E⁗ or F⁗), be excluded. Exceptional voices have a range far greater than two octaves. Falsetto voice is produced by throwing half of the vocal cord out of vibration (the way in which this is accomplished is not clear), and at the same time raising the back of the tongue to the wall of the throat in such a manner as to cut off all the lower part of the upper resonating chamber, leaving it only the mouth and the cavities of the nose.

So far the mechanism of voice is easily understood. As the scale is ascended, the vocal cords are progressively tightened by the contraction of the crico-thyroid muscles. But an analysis of the feelings experienced during singing (and of the quality of the sounds produced) shows that by themselves these muscles are not able to make changes in the tension of the cords sufficient to account for the full range of the voice. Or, put in another way, the tension of the vocal cords is not altered to the extent which would be necessary if upon it alone depended a range of from two to three octaves. It is obvious that by some means the length or thickness, or both, of the portions of the cords vibrating is changed as the scale is ascended. If commencement be made on a low note, a point is reached, after a certain number of notes have been sung, at which a sudden change occurs. There is an alteration in the quality of sound, the more marked, the less well trained the singer. The singer experiences a feeling of relief. If a finger be placed on his crico-thyroid muscle, a relaxation of its anterior fibres can be detected. As he proceeds up the scale, these fibres again tighten. At a certain point there is again a change in the quality of voice, and in the feelings which accompany its production. The two points at which change occurs are said to divide the voice into three “registers”—the lower, or chest-register, the middle, and the upper, or head-register. A great effort is needed to hold either register above its natural range.

The physiology of the registers is a subject far too thorny for handling in this book. The larynx can be watched with the laryngoscope during the production of notes of different pitch, but observers are not in accord regarding the appearances which it presents, or their interpretation. The possibilities of changing the reed which vibrates, the vocal cord, otherwise than by increasing the direct pull upon it exerted by the crico-thyroid muscle, appear to be as follows: (1) During the production of the lowest notes the elastic portion of the arytenoid cartilage may be included with the cord. It may be thrown out of vibration by its rotation inwards (under the action of the lateral crico-arytenoid muscle) until it is pressed against its fellow. (2) Certain portions of the cord may be damped by partial contractions of the internal thyro-arytenoid muscle. It has been frequently stated, although the statement is not accepted by all anatomists, that some of the fibres which take origin from the arytenoid cartilage end in the cord, instead of passing right through to the thyroid. It is supposed that by their contraction they throw the posterior portion of the cord—even, it is asserted, as much as its posterior two-thirds in the higher head-notes—out of vibration. (3) It appears that the width (thickness) of the cord vibrating is also regulated by the contraction of the thyro-arytenoid muscle. Those who regard the diminution in the thickness and width of the vibrating fold of mucous membrane and underlying elastic tissue as the chief factor in the adaptation of the larynx for the middle register lay great stress upon the sense of relief from muscular effort which accompanies the transition. Less force is needed to tighten the thinner cord. They also call attention to the loss in volume of the voice when the lower register is left, and to its greater softness. The lower is spoken of as the thick register, the middle as thin, and the upper (on the hypothesis that part only of the cord vibrates) as the small register.

Singing reveals the possibilities of the larynx as a musical instrument. In =speech= the larynx plays a part, but the form of the syllabic sounds and the relative prominence of overtones in the vowels is of more importance than pitch. Flexibility of voice is dependent upon ability to increase or diminish at will the size of the resonating chambers of the throat, mouth, and nose, or the freedom of access to them. Conversation is carried on in the lower or chest-register. When a practised speaker mounts a platform, he spends the first few minutes in ascertaining the pitch of the hall—that is to say, the pitch of his voice to which the room resonates most freely. Having found the proper tone, he endeavours to maintain a uniform tension of his vocal cords, and therefore a uniform pitch. He relieves the monotony of speech by suitable variations of its overtones. Nothing is more uncomfortable to listen to than an oration delivered in cadences. The speaking voice should be full, round, and musical, and free from affectation—as guiltless of the intoning or preaching quality as it is of harshness or of vulgar flatness. A flexible voice is capable of producing, as occasion calls for them, tones of any and every quality. With the throat and mouth set for the syllable “haw,” it is impossible to do justice to such words as “king” and “queen.” The voice-tones of a superior person are as distasteful to the hearer as those of a vulgarian. Unpleasant also is a nasal twang, illogically so called, since it is due, not to the opening of the resonating chambers of the nose, but to the restriction of the entry of air into them. In this it is somewhat similar to the effect produced by a severe cold. Resonance in the nasal chambers produces a clear, ringing voice.

A little consideration of the varying qualities of different voices suffices to show how largely they depend on resonance. When vowel-sounds are analysed, it is found that the distinctive character of each of them is dependent upon the overtones which it contains. For every vowel the overtones are fixed, or very nearly so, no matter what may be the pitch of the note to which the vowel is sounded.

It is much to be regretted that the alphabet was settled before the physiology of speech was understood. Were it based upon reasonable principles, children would be spared the bewilderment which overtakes them when they endeavour to establish in their minds some kind of relation between the names of consonants and their effects upon the blast of air as it passes through throat and mouth, and between tongue and palate, teeth and lips. The vowels, had physiologists defined them, would have been real pure vowel-tones—_ōō_, _o_, _ah_, _ēē_—sounds which can be sustained for an indefinite time, and allowed to die away without deterioration in their quality. _A_ (_é_ as pronounced in France) is doubtfully pure—it has a tendency to tail off in _ēē_; _ī_ is frankly a diphthong, _ai_ (_ah-ēē_). Try to hold a long final note on the syllable “nigh”! An international standard of vowel-sounds would have been fixed, by giving the vibrating periods of the tuning-forks for which in each several case the resonating chambers are shaped, and defining the relative accentuation of each overtone. Greatest boon of all, the irruption of the Essex dialect would have been dammed. It would not have been allowed to inundate London, or to submerge Australia, debasing our English tongue. In Cockney speech vowels degenerate down the line of greatest indolence. _Aw_ becomes _or_, or _ar_; _a_ becomes _i_. It requires a greater effort to pronounce a full _a_ than a flat _a_, a definite flat _a_ than _i_. And worse than a Cockney’s unwillingness to take the trouble necessary for the production of dignifiedvowel-tones is his reluctance to make the effort required for the holding of any tone. In his mouth virile, self-reliant vowels are replaced by emasculated diphthongs, which collapse as they present themselves to the ear. It costs trouble to fix the mouth-chamber before a vowel is sounded and to hold it steady until it is finished. _Ah_ slides down through _ai_ to _ēē_; _i_ slips into _ēē_. “Cow” becomes _kyow_; “you,” _ye-u-ow_; “cart,” _kyart_. And just as the effort needed for the filling of the vowels is shirked, so also is grudged the expenditure of an accessory blast for their aspiration.

When a vowel is whispered, although the vocal cords do not vibrate, the blast passing through the resonating chambers produces the overtones characteristic of the vowel. Anyone who feels his own larynx while he sings, to the same note, the various vowels between _ōō_ and _ēē_—he may please himself as to the number of _ai_, _eu_, and _ŭ_ vowels he interposes between these two extremes—will recognize that it is pulled farther and farther upwards by the muscles which surround it. The cavity of the mouth is at the same time made shorter and broader for each succeeding vowel. Singing the several vowels before a piano, and at the same time striking various keys, it is felt in the mouth that the resonance of that chamber is reinforced by certain selected notes. Certain tuning-forks, when sounded in front of the mouth shaped for a vowel, ring out more loudly, because the mouth-cavity resonates to their prime tones. The overtones of the vowels can be analysed in this way. Conversely, by sounding simultaneously an appropriate selection of tuning-forks, each with the right degree of force, the overtones of a vowel can be synthesised. Thus if whilst one tuning-fork is sounding B₁♭ (B♭ above middle C), two others be added giving B₂♭ (loud) and F₃ (soft), the composite sound resembles the vowel _o_. If to these same three forks, with F₃ sounding more strongly, B₃♭ and a loud D₄ be added, the sound changes to _ah_.

The organ of voice is a combination of a reed-pipe with resonating chambers, the shape of which can be changed at will. The quality characteristic of a vowel is given to it by adding to the note produced in the larynx sounds due to the resonance of the throat and mouth. On the assumption (not allowed by all authorities) that, since the resonating chambers are not sound-producers, they can only add to the larynx-tone, as “formants” of a vowel, its own harmonics—sounds which they have picked out of it—it follows that, if, when the prime is changed, the resonators were not adapted to the new note, they would be dumb. If this attitude in regard to the question be justified, there must be a certain amount of variation in the quality of a vowel as the scale is ascended. But a vowel is not a musical tone; it is a conventional sound. Its whole value depends upon its retaining, as nearly as may be, the same quality, whatever be the pitch of its prime tone. By adjusting the form of the throat and mouth, we can not only prevent one vowel from passing into another, but we can keep it so nearly true to itself as to convince the ear that its quality is unchanged: _ōō_ remains _ōō_, and _ah_ _ah_, although the form of the sound as produced on C♯ is different to its form when sung to C.

Apart from the general distinction that low notes are taken more easily with vowels requiring a large mouth-cavity, and high notes with those providing a small one, there are certain very distinct relations between vowel-sounds and musical tones which need to be borne in mind in setting words to music. A singer changes a word when he feels that its vowel-tone does not allow him to give to the note to which it is set the fullest expression of which he is capable.

An account of the physiology of the production of consonants is to be found in most text-books of grammar.

FOOTNOTE:

[3] A bullock’s larynx is an admirable object of study. In almost all points of form and structure it is practically identical with the human larynx, and its large size makes it easy to dissect.

INDEX

Absorption from alimentary canal, 129 Accelerator nerves of heart, 237 Accommodation of the eye for distance, 391 for light, 390 Acromegaly, 93 Addison’s disease, 91 Adrenalin, action on the kidney, 209 formed in suprarenal capsule, 92 Air, quantity inspired, 173 quantity needed by individual, 191 Air-cells of lungs, 168 Albumin made by plants, 12 Alcohol, effect on nerve conduction, 301 Alimentary canal, morphology of, 98 nerves of, 104 Altitude, highest, attained by climbers, 187 Alveoli of lungs, their number, 169 Amides produced from proteins, 119 Amœba, irritability of its protoplasm, 10 Amyl nitrite, effect on vascular system, 237 Anæmia, treatment with iron, 67 Anæsthetics, influence on protoplasm, 11 Analysis by animals, 12 Angina pectoris, 237 Angler fish, its nerve-cells, 31 Animal machine and its driver, 354, 358 Animals, hunting _versus_ hunted, 366 not reflex machines, 358 relative insensibility to the knife, 361 Antitoxins, formation by protoplasm, 20 Aorta, diameter of, 232 Aphasia, 352 Apnœa, condition of arrested respiration, 181 Appendicitis, increased frequency of, 101 Appetite, a safe guide, 114 Arteries, blood-pressure in, 234, 239 structure of wall of, 233 Artificial respiration, 183 Asphyxia, 182 Association-zones in the cortex of the great brain, 348 Asthma, due to reflex contraction of small bronchi, 167 Astigmatism, correction by glasses, 393 due to modern print, 269 Attention, effect of, in heightening pain, 361

Bacteria, diminution of number in intestine on milk diet, 138 of alimentary canal, 135 of Bulgarian sour milk, 138 of the River Ganges, 141 in an infant’s intestine, 136 their rôle in nature, 20 Balance-sheet of body, how drawn up, 149 Balloon, highest altitude attained in, 187 Basket-cells in nervous system, 324, 340 Bat’s squeak, number of vibrations, 418 Bats, flight not dependent on vision, 381 Beats in music, explanation of, 407 Beetle, muscle of, 261 Belladonna, physiological action, 109 Bile, composition, 117 function in regard to absorption of fat, 133 relation to digestion, 117 Bile-pigment, origin from hæmoglobin, 69, 82, 118 Bioplasm, the essential substance of a living cell, 148 Birds, sense of hearing of, 410 Blind spot, how filled in, 395 Blisters, 41 Blood, amount ejected by heart, 219 circulation-time, 219 composition of, 59 gases of, amount, 190 tension, 61 lodged in abdominal veins, 234, 236 Blood-corpuscles, cellular nature, 28 life-story, 62 number, 61 origin, 63, 64 structure, 60 Blood-platelets, 74 Blood-poisoning, 57 Blushing, 243 Bowman’s description of kidney, 200 discs in muscle, 259 Brain. _Cf._ Cerebellum, Cortex of cerebrum blood-supply of, 352 Bread, digestion of, 120 Breathing, mechanism of, 171 Bruises, explanation of play of colours, 69 Bulgarian milk-germ, 138

Capillary vessels, circulation of blood in, 232 migration of leucocytes from, 232 structure of their walls, 38 Carbohydrate foods, chemical composition, 147 Carbonic acid, carried by blood, 60 liberation in lungs, 61, 189 Carbonic oxide, compound with hæmoglobin, 187 Carnivora, absorption of fat from alimentary canal of, 133 Cartilage, growth, 28 Catalysis, 17 Cell theory, 26 Cells, constituent parts, 26, 28 size, 30 specialization of function in, 35 Cells of Purkinje in the cerebellum, 303, 340 Cellulose, digestion of, 137 Cerebellum, cases of deficiency of, 341 connections with cerebro-spinal axis, 340 development of granules of, 299, 303 lobes, 338 minute anatomy, 339 phylogeny, 338 relation to tone of muscles, 342 Cerebral hemisphere, an outgrowth towards olfactory pit, 334 in animals with various sensory endowments, 349 Cerebro-spinal fluid, 50 Chemical activity of protoplasm, 12 messengers, 89, 123 processes in plants, 15 Chemiotaxis of leucocytes, 56, 364 Children, brain in, 346 development of astigmatism in eyes of, 269 Chill, catching a, 242 Chloroform. _Cf._ Anæsthetics Cholesterin, 118 Chromatolysis in nerve-cells, 320 Chrome-silver method of colouring nerve-tissue, 293 Chyme, food converted into, 126 Circulation of the blood, 218 Circulation-time, 219 Cirrhosis of liver, 42 Coagulation of blood, 69 Cochlea, anatomy, 413 Cockney dialect, the degradation of vowel-sounds, 439 Coke-fire, poisonous fumes from, 186 Cold-spots in skin, 429 Collaterals of nerves, 297 Colon, length and disposition of, 101 Colour-blindness, 385 Colour-vision, 385 Colours, reason for apparent fading in twilight, 378 Conductivity of protoplasm, 248 Consciousness, does not come within physiological investigation, 360 its part in animal life, 359 Control experiments, their value, 72 Convolutions of brain, 345 Cooking, effect upon digestibility of meat, 120 Corneal epithelium, sensitiveness of, 424 Corpus striatum of brain, 344 Cortex of cerebrum, discovery of excitability of, 344 fissures and convolutions, 345 functional areas, 352 myelination of its fibres, 345 sensory and association areas, 346 structure of, 347 variations in different animals, 349 Corti, organ of, its structure, 414 theories of function of, 416 Coughing, mechanism of, 180 Crayfish, tone of claw-muscle of, 273 Cretinism, 85, 90 Cricket, chirp of, 261 Crypts of Lieberkühn, 103 Curdling of milk, 75

Dancing, association of sound with movement, 422 Day’s work, food required for, 151 Deafness due to sore throat, 412 Degeneration of nerves after section, 326 Depressor nerve of the heart, 237 Diabetes, excretion of more carbohydrate than contained in food, 143 Dialysis, explanation of the process, 40, 128 Diaphragm, function in respiration, 171 Diastases, destructive ferments, 18 Diet, limits of possible variations in, 153 of labouring classes, 152 Digestibility of bread, meat, fish, etc., 120, 125 Digestion, mechanism of, 96 vascular changes during, 235 waits on appetite, 114 Digitalis, action on heart and kidney, 209 Diphtheria, antitoxin of, 20 Diuretics, 209 Dog’s sense of smell, 370 Dreams, theory of, 362 Dropsy, 42 Drowning, resuscitation from, 183 Drugs, physiology of, 95 Ductless glands, 94 Dyspnœa, difficult respiration, 181

Ear, anatomy, 411 bones of, 412 differentiation into separate sense-organs, 410 in fishes, 410 phylogeny, 409 Eel’s blood injected into mammal, 20 Effector, an organ which exhibits change in response to stimulation, 253 Egg-albumin destroyed by blood, 19 Electric organs, 288 phenomena of muscles, 279 Emotions, their relation to vaso-motor changes, 242 Energy, expended by body, 151 source of the body’s, 152 of stimulus compared with energy of muscular response, 254 Engines, body compared with, 152, 256 Epiglottis during swallowing, 433 Equilibrium, maintenance of, in walking, 342 Erepsin, ferment of intestinal juice, 119 Errors of sensory judgment, 402 Excretion, 195 Eye, accommodation for distance, 391 adaptation for darkness, 390 blind spot, 394 optical defects of, 393 phylogeny, 334 refractive media, formation of image by, 391 Eyeball, abnormalities in shape of, 392 anatomy, 373 development, 374 muscles of, indefatigable, 269

Fat, absorption of, 131, 132 accumulation of, relation to foods consumed, 144 chemistry, 132 digestion, 133 laid down in connective tissues, 145 stored in liver, 145 Fatigue, causes of, 45, 268 Fermentation, 16 Ferments, chemical nature, 18 classification, 16, 18 physiological importance, 18 Fibrin of blood, its antecedents, 75 Fireflies, source of their light, 291 Fish, sense of smell of, 365 supposed to be frightened by noise, 410 Flatulence, cause of, 114, 125, 136 Foods, classification, 142 history of, after absorption, 142 relative value, 147, 151, 153, 157 residue after digestion and absorption, 194 Foramen ovale of heart, sometimes perforate, 218 Frigate-bird, turbinate bones of, 166 Frog, supposed to be found entombed in rock, 164 Functional interdependence of organs, 94 Functions transferred to other organs, 87

Gall-stones, cause of formation of, 118 Galvani’s observation of contraction of a frog’s muscles, 277 Ganges, purifying water of, 138 Ganglia of sympathetic chain, function, 325 Ganglion-cells of retina, 376 spinal, 299, 333 Gaseous tension, meaning of expression, 188 Gases of blood, their exchange in the lungs, 184 Gastric glands, structure, 123 juice, amount secreted, 114 composition, 114 digestive action, 115 Gelatin as article of diet, 158 Giant cells, 65 Glands, vaso-motor nerves of, 109, 241 Glycogen, formula, 147 as muscle food, 148 stored in liver, 147 Goitre, cause of, 84 Granules, appearance of, in glands, 110 of cerebellum, development of, 299, 303 Grey matter, formation of paths in, 356 Growth, a function of protoplasm, 24 a reaction to work, 47

Hæmatin, 68 Hæmatoidin, 68 Hæmochromogen, 68 Hæmoglobin, crystalline form, 66, 186 formula, 66 as oxygen carrier, 66, 186 spectrum, 68, 185 Hæmophilia, non-coagulability of blood, 76 Hallucinations, 362 Headache, a pain in the scalp, 106, 319 the brain’s warning of fatigue, 269 from strain of eye-muscles, 268 Hearing, analysis of compound vibrations, 405 capacity dependent upon education, 422 Hearing, Helmholtz’s theory of analysis of sounds, 419 range of sensations, 418 sense of, 404 upper limit, 418 Heart, anatomy, 217 automatism of, 238 development, 218 murmurs, 229 muscular tissue, minute structure, 261 nerves regulating beat, 237, 239 sounds of, 228 valves, their mechanism, 226 work done by, 219, 223 Heat, production of, by muscles, 254, 256 Heat-spots in skin, 429 Helmholtz’s theory of organ of Corti, 419 Hering’s theory of colour-vision, 388 Hormones, meaning of term, 89, 124 of pancreas and liver, 127 of stomach, 123 Humours in ancient medical theory, 79 Hunter, experiment of grafting cock’s spur in its comb, 47 Hydrochloric acid, part taken in digestion, 114 Hydrophobia, protective inoculation, 78 Hyperpnœa, excessive respiratory efforts, 182 Hypoblast, a layer of the embryo, 97

Illusions of movement, 335, 384 of size and distance, 400 Immunity, acquisition of, 20 Impulse of the heart, 225 rate of passage in muscle, 280 in nerve, 278, 280 theory of nerve conduction, 282 Inhibition, explanation of term, 311 of reflex actions, 311 Insects, efficiency of their muscles, 261 Instinct, due to brain-pattern, 359 Intelligence of animals, 359 Internal secretions, 83 Intestinal juice, digestive action, 119 Intestine, large, sacculation of its walls, 101 small, folds and glands of mucous membrane, 102 Intestines, movements of, 103 nerves of, 105 size and situation, 100 Iodine, importance of, to economy, 89 Iodothyrin, goitre due to deficiency of, 90 Iris, its function in regulating admission of light to eye, 394 Iron in food, 67 in hæmoglobin, 67 use of, in treatment of anæmia, 67 Irritability, a function of protoplasm, 10

Japanese, cultivation of sense of smell by, 370 Judgment of angles, 402 of distance and size, 401 of meaning of sensations, 396, 399

Kidney, ancestral history, 195 elimination of indigo by, 207 of birds and reptiles, 200, 207 hydrostatic mechanism, 189 minute anatomy, 196 Kinæsthetic sensations, absence from dreams, 363 part played by, in voluntary actions, 354 representation in cortex of brain, 350, 352 Knee-jerk, 274

Labyrinth of ear, 413 Lactate of ammonia, relation to urea, 13 Lacteals, lymphatic vessels of alimentary canal, 43, 131 Lactic acid produced in muscle, 46, 146 Larynx, closure during swallowing, 433 structure of, 430 Latent period of muscle after nervous impulse reaches it, 278 Laughter, respiratory mechanism of, 180 Lecithin produced by metabolism of nerve-tissue, 118 Leech, ganglion-cells of, 298 Leucocytes as protective agents, 52 death of, 54, 57 migration of, 49 number in lymph and in blood, 49, 61 origin of, 33, 51 source of fibrin-ferment, 74 Leucocythæmia, excess of leucocytes in the blood, 215 Levers to which muscles are attached, 286 Light, emission of, by animals, 291 Lime, influence upon coagulation of blood, 75 curdling of milk, 75 Lithates, or urates, constituents of calculi, 213 Liver, destruction of red blood-corpuscles in, 83 form and structure of, 160 former theories of its functions, 129, 163 manufactures urea and uric acid, 146, 162 of well fed sheep, 147 origin of, in vertebrate phylogeny, 34 Liver stores food, especially glycogen, 46, 145, 147, 161 Locomotor ataxy, 341 Ludwig’s view of mechanism of kidney, 200 Luminous glands, 291 Lung, exchange of gases in, 173, 184, 190 nerve-supply, 178 structure, 168 Lymph, amount of, in body, 37 composition, 49 relation to blood, 51 Lymph-spaces, 37, 43, 49 Lymphatic glands, structure of, 54 Lymphatic vessels, 43

Malapterurus, electric organs, 288 immense neurones of, 295 Manometer for measuring blood-pressure, description of, 238 Man’s ancestry, 153 Massage of abdominal viscera, 101 of muscles, 48 Meal, the story of a, 120 Meat, diet consisting solely of, 157 digestion of, 121 extracts of, as articles of diet, 159 Megacaryocytes, 65 Memory, physiological explanation, 356 Metabolism, chemical change in living tissue, 12, 273 Methæmoglobin, 69 Microscope, its discovery, 26 Migration of birds, 359 Milk, call for secretion of, by a hormone, 94 chemical and physical constitution, 132 digestion of, 127 Milk diet, reduction of bacteria in alimentary canal on, 138 Mind, physiology of, 354 Mosquitoes, production of sound by, 261 Motile cells, 32 Mountain sickness, 187 Mountains, highest climbed, 187 Mucous membrane, use of term, 97 Murmurs, in chest, in diseases of lungs, 169 of heart, 229 Muscle, change in appearance under microscope during contraction, 263 chemistry of contraction, 266 contraction a phenomenon of osmosis, 258 electric phenomena of, 278 means of promoting growth of, 271 measurement of its power, 285 nature of impulse which leads to contraction of, 282 Muscle of heart, its minute structure, 224 of insects, its efficiency, 261 plain, its minute structure, 258 plasma, its coagulation, 266 rhythm of voluntary contraction, 279 theory of its structure as a mechanism liberating energy, 234, 255 tone of, 272 tracings taken of contracting, 278 voluntary, its minute structure, 259 wastes when its nerve is severed, 274 work done by, proportional to load, 286 Muscles, arrangement in regard to the bones which they move, 286 co-operation in lifting a weight, 287 Muscular energy, source of, 235 Muscularis mucosæ of alimentary canal, 103 Musculi papillares of heart, 227 Music, chords admissible in, 408 Indian, division of octave, 408 primitive, prevalence of minor chords, 408 Musical tones and overtones, 406 Myelination of nerves, order of, 345 Myxœdema, dependent on disease of thyroid gland, 85 Myxomycetes, fusion of cell-bodies of, 27

Nasal chambers, air warmed in, 166 Negroes, their long heels, 285 Nerve, conduction in, theory of, 282 degeneration, 326 electrical phenomena, 279 indefatigable, 282 regeneration, 326 structure, 296 Nerves, depressor, 237 experiment of crossing, 327 fifth, 316 of heart, 239 of intestines, 426 protopathic and critical systems of, 425 secretory, of the salivary glands, 109 splanchnic, 236 superior laryngeal, 178 vagus, 104 vaso-motor, 239 Nerve-cells last throughout life, 148 limitations of their functions, 321 store of energy in, 320 transfer of impulses from cell to cell, 177, 300 their relation to muscle-fibres, 274 varying size of, 295, 322 Nerve-centres, 176 Nerve-force, improper use of expression, 281 Nerve-impulses, distribution in grey matter, 305 reinforcement of, 320 resistance to, at synapses, 306 Nerve-nets, pericellular, 301, 319 Nervous system, neuronic and extra-neuronic conduction, 310 phylogeny of, 332 Neuro-fibrillæ, 298 Neurone, origin of term, 293 transmission of current by, 328 various types of, 296, 323 Night-blindness, 378 Nissl’s bodies, source of nervous energy, 320 Nitric oxide, combination with hæmoglobin, 186 Nitrogenous equilibrium, 150 food, stimulating effect of, 157 waste, 210 _Nœud vital_ of Flourens, 176 Normal diet, 151 Normal salt-solution, 82 Nucleo-proteins, source of uric acid, 215

Odours, classification of, 366 Œdema, or dropsy, 42 Olfactory membrane, structure, 366 Optic nerve, number of fibres, 378 Organ of Corti, structure, 415 theory of function, 417 Organs that have lost their prime functions, 87 Orientation, sense of, 335 Osmosis, 40, 128, 201 cause of muscular contraction, 235 Osteoblasts, bone-forming cells, 32 Osteoclasts, bone-eating cells, 65 Oxygen, amount required per diem, 166 carried by red blood-corpuscles, 66

Pain, influence of, upon action, 359 referred from viscera to surface of body, 316 relation to sensation, 313, 425 theory of, 312, 425 Pancreas, structure, 116 Pancreatic juice, constitution, 116 fat-splitting ferment of, 133 Papillæ of the tongue, various forms of, 97 Parathyroids, 86 Pepsin, digestive action, 115 Peptone prevents coagulation of blood, 77 Pericellular nerve-nets, 301 Perspiration, cools the surface of the body, 236 repressed during fever, 257 Peyer’s patches of lymph-follicles in intestine, 53 Phagocytes, germ-eating leucocytes, 60 consumption of red blood-corpuscles by, 82 Phosphenes, developed by pressure on eyeball, 383 Phosphorescence, cause of, 291 Phrenology, 343 Pictures, suggestion of solidity in, 401 Pineal body, phylogeny, 334 Pituitary body, 93 Plants, anæsthetized by ether, 12, 24 their metabolism, 15 their respiration, 24 Pleura, lining membrane of chest, 172 Pleurisy, pain of, 313 Pleuritic fluid, absorption of, 223 Pneumonia, changes in lung during, 169 Portal system of bloodvessels, 80 regulator of vascular tone, 236 Power of muscles, 285 Precipitins formed in blood, 19 Proteins, absorption by alimentary canal, 145 chemical constitution, 6 dietetic value, 157 fate after absorption, 212 Protopathic nerves, 425 Protoplasm, arrangement in cells, 30 constitution, 7 Huxley’s definition, 6 Pulse, cause of, 244 records of, 245 variations, 247 Purgatives, theory of action, 128 Purkinje-cells of cerebellum, 303, 340 shadows of retinal vessels, 375 Pus, origin of, from leucocytes, 57 Pyramids of cortex of great brain, 346

Rabbit’s ear, vaso-motor changes in, 235 Receptor, an organ specially sensitive to stimulation, 253 Referred pains from viscera, 316 Reflex action, inhibition of, 311 of scratching, 330 vinegar experiment with frog, 307 Regeneration of nerves, 326 Renal-portal circulation, 199 Renewal of tissues, 148 Rennin, ferment of milk, 16 Resistance in nervous system, laws of, 177, 307 Respiration, artificial, 179 effect on circulation, 221 a function of protoplasm, 23, 164 movements of, 171 nervous mechanism, 175, 179 in tissues, 165, 193 Respiratory centre in medulla oblongata, 176, 178, 182 Respiratory quotient, 174 Retina, structure, 374 Retinal pigment, relation to vision, 381 Rice ordeal, arrest of secretion of saliva, 112 Rigor mortis, 266 Rods and cones, respective functions in vision, 378 Rowing, value of, as exercise, 287

Saccharin, taste of, 367 Saline frog, respiration in, 193 Saliva, chemical constitution, 107 function of, 96, 107 Salivary glands, mechanism of secretion, 108 nerves of, 109, 236 Salts, absorption of, in alimentary canal, 128 Scientific method, definition of, 71 Scratch reflex, in dog, 330 Sea-sickness, 106 Secretin, hormone of pancreas and liver, 127 Secretion, accumulation of granules in cells, and their discharge, 110 a response to stimulation, 111 not a process of filtration, 110 Semicircular canals, their functions, 410 their positions in space, 335 Sensations, their apparent fusion, 356 many which escape attention, 318, 355 neutralization of one by another, 356 Sense-organs, origin in vertebrata, 336 Sensory areas in cortex of the great brain, 348 Sensory nerves, their connection with cerebro-spinal axis, 304 Shell-fish, poisonous extract of, 41 Shivering due to loss of heat from skin, 257 Sight. _Cf._ Vision Skate, electric organs of, 289 Skilled movements, dependent upon kinæsthetic sensations, 357 Skin, experiment of cutting nerve, 424 variety of sensations from, 423 Sleep, condition of neurones in, 362 Sleeping sickness, 33 Smallpox, protection against, 78 Smell, disappearance of sense of, in later life, 370 dog’s dependence upon sense of, 366 reason for mental associations with sensations of, 371 sensitiveness to mercaptan, 365 Smells, nice and nasty, 369 Smoking, mental effect of, 371 Sneezing on looking at bright light, 317 Sore throat, cause of deafness, 412 Soul, Aristotle’s definition, 32 Sound, mode of conduction, 404 rapidity of vibrations of, 406, 418 Sounds of the heart, 228 periodic and aperiodic, 409 Spectacles, defects of eyeball which call for, 392 Speech, derangements of, due to disease of the brain, 353 mechanism of, 437 Sphygmographs for recording pulse, 245 Spinal dog, reflex action in, 330 frog, reflex action in, 307 ganglia, development of cells, 299 Splanchnic nerves, regulation of blood-pressure by, 236 Spleen, destruction of blood-corpuscles in, 80 structure, 79 Squint, correction of double vision in, 397 Starch, formula, 15 Star-shapes due to puckering of crystalline lens, 393 Starvation, statistics of, 156 Stiffness of muscles, cause of, 45, 271 Stimuli to muscles and nerves, 248 Stokes, discovery of spectrum of blood, 68 Stomach, digestion in, 120 glands of, 123 referred pains from, 316 shape and size, 99 Stone in the bladder, its cause, 213 Subconscious self, 355 Sugars, digestion of, 120, 136 formulæ, 15 Sun, apparent size near horizon, 399 Suprarenal capsules, their structure and function, 91 Sweetbread as article of diet, 215 Sympathetic system of nerves, 243, 325 diameter of fibres, 325 Synapses of nerve-cells, resistance interposed at, 306 Synaptases, constructive ferments, 18 Synthesis by plants, 15

Tapeworms, resist digestion in the intestines, 21 Taste, confusion with sense of smell, 364 localization on tongue, 367 sense of, in fishes, 365 sensitiveness to quinine, 369 Taste-bulbs, their structure, 368 Tattooing, removal of pigment by leucocytes, 55 Tea, its dietetic value, 122 Teeth, 96 Tendon, the growth of, from cells, 28 Tension of gases in the lungs, 190 Tetanus, the vibratile contraction of muscle, 279 Thoracic duct, discharges lymph into veins, 43, 131 Thorax, negative pressure in, 222 Thorns on dendrites of nerve-cells, 300 Thyroid body or gland, forms an internal secretion, 86 relation to goitre, 85 structure of, 85 Tight-lacing, deformation of organs which it causes, 220 Tigroids, in nerve-cells, stores of energy, 320 Tissues, respiration in, 165, 193 Tone of muscles, 272 Tongue, as organ of taste, 367 Tonsils, function as guardians of the fauces, 53 structure, 52 Torpedo, electric organs of, 290 Touch, sensations of, 426 Toxins produced by microbes, 20

Urea, amount relatively to proteins consumed, 155 antecedents of, 146, 212 chemical formula, 211 secreted during period of starvation, 156 Uric acid, amount secreted daily, 213 artificial production of, 13 chemical formula, 13, 214 diathesis, its relation to diet, 140 due to metabolism of leucocytes, 53, 216 form in which excreted, 207 made in the liver of birds, 13 Urticaria due to abnormal composition of lymph, 41

Vaccination, protective value of, 22 Valves of heart, their mechanism, 226 Vascular system, tone of, 236, 240 Vaso-constrictor nerves, 236 Vaso-dilator nerves, 236 Vegetables, dietetic value of, 139 digestion of, 125, 137 Vermiform appendix, 88 Villi of intestine, absorption of food by, 130 fat seen in, during active digestion, 134 Viscera, their insensitiveness to injury, 316, 426 Vision, colour contrasts, 382 duration of images, 382 judgment of distance and size, 411 solidity, 401 stereoscopic, doctrine of corresponding points, 397 Visual purple, 381 Vital action, definition of expression, 205 Vivisection, 4 Vocal cords, structure, 431 how modified in singing, 435 Voice, breaking of, in boys, 434 falsetto, how produced, 435 range of human, 435 registers, 436 Vomiting, 105 Vowels, synthesis by tuning-forks, 439

Wandering cells, 33 Warmth, appreciation of, by skin, 429 Waste substances, classification, 194 how eliminated from body, 59 Waterfall, negative after-image of, 384 Water-weed, experiment proving that it respires, 24 Wear and tear of bioplasm, 145 Wisdom-tooth, tending to disappear, 96

Yawning, beneficial effect on circulation, 222 nervous mechanism of, 180 Young’s theory of colour-vision, 385

Zymogen, 110

THE END

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