will be necessary to describe the histological. The reader may have
already wondered how we managed to find out so much about the cellular
structure of the body. It is no easy matter to cut up soft tissue,
of the consistency of an unboiled egg, into thin slices which can be
examined under the microscope. It is done in the following manner: The
bloodvessels of the freshly killed body are injected with a fluid which
instantaneously kills and fixes the cells in much the same way as an
egg is fixed by being hard-boiled. The natural shape of the cells is
thus preserved, and the loss of any of their chemical constituents by
putrefaction prevented. The piece of organ is then impregnated with
and cast in the middle of a solid block of paraffin wax, which is put
into a machine and shaved up into thin slices, about 40,000 to the inch
sometimes. One of these shavings is then stuck upon a glass slide, and
on the wax being dissolved away with some such substance as benzine, a
section of the tissue, about one cell thick, is left on the glass ready
for microscopic survey.
To do anything like justice to the histological methods would require
a volume in itself. When the sections are fixed upon slides, they are
treated with a number of reagents to show their chemical and structural
peculiarities. One section is stained specially to show the nucleus;
another to show the centrosome; another zymogen granules, etc. And, as
all these cannot be shown at their best in one cell, the differently
treated sections have to be separately drawn or photographed, and the
typical structure compiled from several. By careful staining, the
chemical composition of the different parts of the cell is being worked
out, and the effects of rest, activity, feeding, and other influences,
studied.
Take as an example the effects of a meal. A number of animals of the
same litter are fed together out of the same trough. One has been killed
before the meal, and the rest are killed at intervals dividing the
time which must intervene before their next feeding-time comes round.
Series of sections from their organs are prepared, one from each animal
being mounted in order upon the same piece of glass, dipped in the
same reagents, and examined under the same microscope. From a number
of these sections the progressive effects of a meal upon each of the
several constituents of the cell are traced out, and some of the chemical
processes deduced.
Turning to the physical side of physiology, it is unnecessary here to say
more about the means employed for studying the properties of muscle and
nerve than that many of the phenomena occur with such extreme rapidity
that they can only be perceived by the photographic plate. In the study
of the large organs, the physiologist finds a fascinating employment in
devising models in which, so far as possible, all the physical conditions
are reproduced, and this not only for the benefit of his pupils, but to
help himself in perceiving their meaning. Too much reliance must not be
placed on these models, of course, but they have added considerably to
our knowledge of the eye and throat.
It requires no great imagination to perceive the difficulties which lie
in the way of studying the nervous system. Tracing nerve fibres under
the microscope through interminable series of sections is a labour which
can neither be hurried nor scamped. It is greatly aided by pathological
specimens. An animal which has been through life with only one eye will
obviously have central organs of vision showing wide contrasts. Those
connected with the blind eye will be undeveloped, because never used,
while the corresponding lobes of the brain connected with the other eye
will show the effects of doing extra work.
Many of the problems which meet the physiologist can only be solved
by experimenting upon a live animal, and these experiments form by
no means the easiest part of his work. The animal must be kept, so
far as possible, under physiological conditions—that is to say, free
from pain and fright and unpoisoned by drugs. Thanks, however, to an
extensive knowledge and skilful use of anæsthetics, the obstacles to
this method of investigation have been overcome, and its results have
proved very profitable. The absence of pain is a very important factor
in an experiment, and even if the physiologist took the wanton delight
in inflicting suffering which the imagination of his enemies attributes
to him, he would have to restrain its indulgence in his laboratory, or
forego the hope of even moderate success. In this country, moreover,
the Government will not allow such experiments without its express
permission, and the license is very rightly only granted to men whose
researches promise an adequate return, and who are likely to conduct them
humanely and successfully.
Physiological research is not a hobby to be lightly taken up. It is not
one merry round of exciting tussles with tortured and infuriated cats
and dogs; on the contrary, it entails arduous labour and needs infinite
patience. The experiments, often tedious in themselves, have to be
repeated again and again in as many different ways as possible, until
every slight difference in result can be accounted for; and the certainty
that both the methods used and the interpretation given will, when
published, receive the closest, and not in every case the friendliest,
scrutiny by other members of the profession serves as an admirable
corrective to jumping at conclusions. It is, however, an occupation of
absorbing interest, and the physiologist feels amply repaid if he can
think that his labours have added, no matter how little, to that control
over Nature which the severe conditions of modern life make every day
more pressingly necessary.
INDEX
A.
Abdominal circulation, 54
Absorption, 25
Acid, hydrochloric, 23
Afferent system of nerves, 92
Alcohol, 95
Alimentary canal, length of, 19
movements of, 46
origin of, 17
structure of, 46
Amœba, 16
Amœboid movement, 31
Amount of food, 15, 96
Animalcula (unicellular micro-organisms), 5, 8, 16, 31, 102, 105
Aorta, 51
Arm, 57
Artery, 48
Association centres, 91
Athletes, 98
Atom, 2
Auditory mechanism, 74
Auricles, 49
B.
Bacteria, 23, 44
Beaumont, 25
Bile, 24, 62
Blind, experiments with the, 100
Blood, 26
circulation of the, 48
clotting after death, 104
corpuscles, 29, 45
course of the, 27, 55
pressure, 51, 66
Body, the, 9, 94
Boils, 45
Bone, 36, 56, 98
Brain, 63, 79, 102
Breathing, 25, 52, 82, 97
C.
Canals, semicircular, 77
Capillaries, 48
Carbohydrate, 14, 96
digestion of, 22
Carbon, 11, 13
Carbonic acid gas, 13, 25
Cartilage, 36
Cavity of the body, 43
Cell, 4
a chemical laboratory, 6
division of, 32, 105
exhaustion of, 102
movements of, 5, 31
nerve, 60, 87
spinal ganglion, 63
Centres, nervous, 63, 78, 88, 91
Centrosome, 31
Cerebellum, 84
Cerebral cortex, 86
hemispheres, 85
Chemical compounds, 2
needs of body, 11
Chemistry of the body, 8
Chords, vocal, 93
Cilia, 33
Circulation, 27, 97
course of, 28, 55
mechanism of, 48
Circulating fluids, 26
Clotting of blood, 104
Cochlea, 76
Cold, 83
Collagen, 24, 35, 96
Compounds, chemical, 2
Conductivity of protoplasm, 59
Connective tissue, 24, 35, 96
Conservation of energy, 92
Contraction of heart, 49
of muscle, 34
Cooking, 96
Cord, spinal, 63, 78
Corpuscles, red blood, 29
white blood (leucocytes), 45
Cortex, 86
Cough, 65, 67
D.
Death, 103
Diaphragm, 52, 97
Diet, 11, 95
Digestion, 11
by body, 22
by cell, 16
Doctor, ix
Drum of ear, 75
E.
Ear, 74
Education, 99
Efferent system of nerves, 92
Egg, white of, 13
Electric manifestations in tissues, 40
organs of fish, 42
stimulation of tissues, 37, 88
Embryo, development of, 17
Endolymph, 74
Enzyme, 15
Epilepsy, 89
Equilibrium, 66, 84
Exercise, 97
Eye, 73
education of, 100
protection of, 65
F.
Fainting, 66
Fat, 14, 24, 27
Fatigue, 40, 102
Ferments, 15
Fibres, connective tissue, 35
muscle, 34
nerve, 42, 60
Fibrils, muscle, 35
Fish, electric, 42
Food, 10, 95
amount of, 15, 96
vacuole, 16
Forehead, 91
Frog experiments on muscle, 37
reflexes, 68
G.
Ganglion, spinal, 62
Gastric juice, 23
Gelatin, 24, 35, 96
Gland cells, 21
Glands, origin of, 20
salivary, 22
sweat, 71
tear, 65
H.
Hæmoglobin, 29
Hair, 70
Harvey, 108
Head, 79
Hearing, 74
Heart, 48, 66
Heat, production of, 13
regulation of, 83
Histological methods, 110
Huxley, 7
Hydrochloric acid, 23
I.
Internal secretion, 29
Intestine, movements of, 47
Involuntary movements, 65
muscle, 34
Iron, 95
K.
Kidneys, 29, 95
L.
Labyrinths of ear, 74
Leucocytes, 42
Limbs, 56
Liver, 24
circulation through, 27, 54
Living matter, 1
Localization of function in the brain, 86, 88
Lungs, 52, 93
absorption by, 25
Lymph, 26
circulation of, 27, 48
M.
Marshall’s fibrils, 35
Meat in diet, 15, 95
Medicine, ix
Medulla (hind-brain), 82
Memory, 91
Micro-organisms, 5, 8, 16, 31, 102, 105
Microscope (histological methods), 110
Milk, 95
Mixture, 3
Molecule, 2
Mouth, 79
Muscle, 34
how studied, 37
of alimentary canal, 46, 95
Muscles, 97
of limbs, 56
stiffening at death of, 104
N.
Nerve cells, 60
centres, 63, 78
fibres, 42, 60
Nervous system, 58
Nitrogen, 12
Nucleus, 4, 21, 32, 106
O.
Olfactory lobe of brain, 85
sense organs, 72
Oxygen, 11, 13, 25, 82, 95
P.
Pain, 91
Pancreas, 24
Paramœcium, 16
Peptone, 24
Perilymph, 74
Peristaltic movements, 24, 63, 95
Physical culture, 98, 101
Physiological methods, 37, 88, 109
Physiology, ix, 107
Pleasure, 91
Pressure, blood, 50, 66
Proteids, 12, 23, 96
Protoplasm (living matter), 1
Pulmonary circulation, 53
R.
Reflex action, 62, 65
centres, 82
Removal of refuse, 27
Rennet, 21, 24
Respiration, 25, 52, 82
Ribs, 52
Rigor mortis, 104
Rutherford’s fibrils, 35
S.
St. Martin, 25
Saliva, 22
Salt, 11, 14, 29
Scavengers of body, 43
Sea-sickness, 78
Secretion, 21
internal, 29
reflex control of, 66
Semicircular canals, 77
Shivering, 83
Sight, 73, 100
Skin, 69
Sleep, 102
Smell, 72, 84
Sneeze, 65
Sound, 76
Speech, 93
Spinal cord, 63, 78
Spirits, 95
Spleen, 27, 54
Standing, 66, 84
Starch, 14, 96
Stomach, 23, 47
Sugar, 14, 96, 102
Sympathetic nervous system, 62
T.
Taste, 72, 84
Tear glands, 65
Temperature, 83
Tendon, 37
Tetanus, 39
Thorax, 52
Thought, 91
Thyroid gland, 29
Trachea, 52
Training, 98
U.
Unicellular animals, 5, 8, 16, 31, 102, 105
V.
Valves of heart, 48, 50
Varieties of protoplasm, 6
Vegetable food, 96
Veins, 48
Ventricles, 49
Veratria, 40
Vision, 73
Voluntary movement, 56
muscle, 34, 56
W.
Walking, 66, 84
Warmth, 83
Water, 95
_Ballière, Tindall and Cox, 8, Henrietta Street, Strand_