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 drawing shows the folds of mucous membrane,
the vocal cords, which stretch from the tips of
the arytenoid cartilages to the recess behind
the median portion of the thyroid cartilage. To
the outer side of each vocal cord is seen the
thyro-arytenoid muscle (cut across), consisting
of a broad outer portion, chiefly concerned in
closing the glottis during the act of swallowing,
and a smaller internal portion, which regulates the
length and the thickness of the segment of the cord
allowed to vibrate.]

The leaf-like structure in front of it is the
epiglottis; the two triangular structures at the
back, the arytenoid cartilages; the white bands
on either side, the vocal cords. A, The glottis
is widely open during inspiration. Arrows show
the lines of action of the muscles which rotate,
and approximate, the cartilages. Attached to
their outer angles, and pulling these angles
forwards, the lateral crico-arytenoid muscles;
pulling them backwards and inwards, the posterior
crico-arytenoid muscles. Drawing the cartilages
together, the arytenoid muscles. B, The glottis
during speaking in a deep chest-voice, or when a
low note of the lower register is being sung. C,
During the production of a high note of the lower
register. D, During the production of a note of the
head-register. E, During the act of swallowing;
the arytenoid cartilages are drawn towards the
epiglottis the aperture is folded into a =T=;
the pharynx (the tube behind the glottis) is
distended.]

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.

From above downwards: the hyoid bone, thyro-hyoid
membrane, thyroid cartilage, cricoid cartilage,
trachea. The upper and posterior angle of the
wing of the thyroid cartilage is suspended from
the hyoid bone; its lower and posterior angle
articulated with the cricoid cartilage. On the
summit of the cricoid cartilage it articulates the
arytenoid. Dotted lines indicate the position of
the vocal cord. The crico-thyroid muscle, which
raises the front of the cricoid, tilting the
arytenoid cartilage backwards and tightening the
vocal cord, extends, fan-like, from the front of
the cricoid to the lower border of the wing of the
thyroid.]

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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