A, the fore-brain is remarkable in that it throws out buds for the two
most important sense organs—those of sight and smell. So important are
these senses, especially in our humble ancestors, as we have already
pointed out, that it is not surprising to find the impressions of the
other senses brought on up from the hinder parts of the brain to be
compared with them. The fore-brain is, in fact, a sort of terminus
whither the whole of the afferent or incoming stimuli are brought, and
whence, since information is only received in order to be acted upon, the
supreme orders to the body issue.
In the fore-brain there are centres for specially governing all the
motor organs; but by a strange arrangement the main root of the brain
is overwhelmed by its own offshoot, the hemisphere, or lobe which gives
rise to the olfactory bud. In fact, so great is the importance of the
sense of smell to an animal whose one object in life is to find food,
that, instead of the hemisphere being subordinate to its parent, it
seems to take over most of the latter’s business, receiving a report
of the sensations collected by it, and sending out orders upon its own
initiative. Yet, unimposing though the history of this division of the
brain may be, it ultimately becomes the seat of consciousness, whereby
the mental processes are carried on, and whence all voluntary movements
spring.
[Illustration: DIAGRAM 62.—SHOWING HOW THE CEREBRAL HEMISPHERES ARE
DEVELOPED FROM A, THE FOREMOST BULB OF THE BRAIN.]
Of course, in order to do this, the hemispheres have to grow
considerably, and thus we find them enveloping the rest of the fore-brain
and swamping it in structure as well as in function. Diagram 62 indicates
how this is done, while Diagram 63 shows roughly the proportion and
position the different parts of the brain ultimately attain. Finally,
Diagram 64, which is rather more realistic, but still much simplified,
presents a view of the organ in the head.
The size of the cerebral hemispheres, compared with the rest of the
brain, is especially remarkable. So, too, is their endeavour to increase
their surface still more by throwing it into deep folds. (See Diagram
64.) These two features vary with the position of the animal in the
scale of development; in man, who stands highest in intelligence and
dexterity, the hemispheres are very large indeed compared with the other
organs, and seamed all over with a maze of winding furrows. Another
remarkable feature is the extreme degree to which specialization is
carried out. Different parts of the body are represented, each by a
small area of the cortex, or surface layer, and we know at what spot on
the cortex such sensations as sight and hearing are perceived, and from
exactly what little patch the impulse to move each limb emanates. In
the accompanying diagrams (65 and 66) these areas are mapped out, their
locality being fixed by the principal folds which act as landmarks on the
surface of the hemisphere.
[Illustration: DIAGRAM 63.—RELATION OF DIFFERENT PARTS OF THE BRAIN.]
There is another important fact which we must not omit to mention in
speaking of this localization: each hemisphere presides over the opposite
side of the body. Early in development the nerve fibres from the eye
cross over to the opposite side of the brain, and the afferent fibres
from the lower parts of the body have accordingly to follow suit. Then,
as the efferent fibres—_i.e._, those which set the muscles in motion—have
to bring about the movements in response to information received, they
must also cross to get back to the side from which it came. So, if a
tumour grows inside the head on the right side, it is the left eye which
becomes sightless, or the left hand which grows numb and powerless,
according to the part of the cortex which is pressed upon.
Perhaps the most interesting part of the whole body is that little band
of the cortex running upwards from behind the temple to the crown of
the head, in which (_cf._ Diagrams 64, 65 and 66) the motor areas of
the limbs, and the perception of those sensations which we have grouped
together and called ‘touch,’ are situated. The minute structure of this
region is roughly shown in section in Diagram 67, as it has been made
out with the microscope; but only a few of the nerve cells are shown,
the connective tissue of feltwork in which they are suspended, and
the bloodvessels by which they are nourished, being left out. All the
structures represented are of course very, very small; the large black
patches which represent cells would really be invisible, and the whole
field of the diagram only a mere speck, to the naked eye.
[Illustration: DIAGRAM 64.—POSITION OF THE BRAIN IN THE HEAD.]
A represents the nerve by which impulses are brought in. It runs straight
up to the surface of the cortex, and there its branches end, interlaced
with those of a many-branched distributing cell (B). The two cells (C
and D) shaped like pyramids, which send up branched processes from their
apexes, receive an impulse from the distributing cell, and transmit it
along the fibre which runs downwards from the middle of their base.
Where the fibre from the smaller one goes to we are not sure—probably
to another part of the brain to insure harmonious working—but the large
pyramidal cell sends its fibre right away through the lower parts of the
brain, passing the cell-stations they contain, on into the spinal cord,
till it reaches the centre there, which immediately works some particular
limb.
[Illustration: DIAGRAM 65.—MAP OF THE CEREBRAL HEMISPHERE, SHOWING THE
AREAS IN WHICH VARIOUS FUNCTIONS ARE LOCALIZED.]
Supposing we anæsthetized somebody, throwing him into deep
unconsciousness, and then opened his skull, laying bare the brain as is
done in Diagram 64, only not quite in such a wholesale manner. If we then
stimulated the part of the brain we are now considering at different
places with electric needles, using a weak induction current, we should
see him moving different members according to the different regions
touched—now an arm, now a leg, now the whole head. If we were to place
the electrodes in the centre for the hand, and then gradually increase
the strength of the current, the activity of the hand centre would throw
other centres into activity. The arm would move next, raising the hand
towards the face. Then the eyes would turn, and the whole head to meet
the hand. Lastly the mouth would open. The movements are those of putting
something into the mouth—the ruling passion strong in unconsciousness.
[Illustration: DIAGRAM 66.—MAP OF THE CEREBRAL HEMISPHERE, SHOWING THE
AREAS IN WHICH VARIOUS FUNCTIONS ARE LOCALIZED.]
Such experiments were, of course, first made upon animals, but they have
been fully verified on the human subject. The story of how this was done
is not, however, a romance with a martyr or a criminal for the central
figure. The _corpus vile_ was not provided by a volunteer, or kidnapped
and bound in a dark cellar, but treated as a patient in the airy wards
of a hospital. With increasing knowledge of the brain, it was found that
epilepsy was cortical in origin. A little piece of the cortex becomes
diseased and hyperexcitable. The sufferer suddenly becomes acutely
conscious of one of his members—a hand or a foot, say—not because there
is anything the matter with it, but because the corresponding area in the
brain is morbidly active, and he refers the sensation to the part from
which it receives its nerves. The next moment the limb begins to twitch,
and the excitement spreading, as in the experiment we described above,
to other centres which are not diseased, they, too, become morbidly
active, and the whole body is thrown into convulsions. This is a disease
which must be checked as soon as possible. The surgeon accordingly lays
bare the part of the brain affected, knowing now where to look; finds the
exact spot which is diseased by reproducing the first twitchings of a fit
by electric stimulation, and removes the source of the trouble.
[Illustration: DIAGRAM 67.—SHOWING THE SYSTEM OF NERVE CELLS IN THE
CORTEX.
A, Afferent fibre; B, distributing cell; C, small pyramidal cell; D,
large pyramidal cell.]
Returning to general considerations, an important point is the way in
which the different centres are connected by fibres, which put them
into relation. The brain may consist of many centres, just as the body
consists of many organs, but both body and brain must live as a whole.
If the heart and lungs get out of harmony there is trouble, and if the
bridge which connects hearing with motion in the brain breaks down, as
occasionally happens for a time in an overworked man, he is mentally at a
discount. He can hear and understand, but he cannot write or talk sense:
he is sane, but quite helpless, and generally very frightened.
Still more important are the intermediate stations and sidings on these
lines of communication, for it is here that the most exhaustive weighing
and comparing of incoming stimuli is carried on—the final balancing
before a voluntary action; in a word, thought.
These courts of inquiry are called association centres. It used to be
believed that they were all in the fore-part of the brain, under the
forehead; but this is evidently not the case. Several men in war or
by accident have had the frontal lobes of their brain damaged beyond
repair; and when they have been discharged from hospital, where, thanks
to the advance made by surgery since anæsthetics and antiseptics were
discovered, they have been successfully treated, they have gone back
to their work seemingly in no way different from men whose brains were
whole. In some cases they have even been reported as having become
quicker and sharper than before, probably owing to there being fewer
association centres, and thought being accelerated by simpler machinery:
facts are thenceforward shaken through a larger-meshed sieve.
A few general considerations, and we have done. There is no centre
for memory in the brain. The facts which we remember are not stored
as in a box, nor can one imagine how they could be, considering that
the physical basis of an idea is molecular change. The whole nervous
system is probably concerned in memory, a particular change, which has
momentarily occurred in its tissues, being more likely to occur again
under certain circumstances than a fresh one, and certain tracks becoming
well beaten and more permeable than others. Pleasure and pain are other
general phenomena: they are not to be localized in the brain like vision
or hearing. Pleasure is the consciousness that the whole body is under
favourable conditions; and pain, the knowledge that the protoplasm of
certain cells of the body is being acted upon by injurious agents,
chemical or physical. There seems to be good evidence that separate
nerves convey impressions of injury, distinct from those of touch and
temperature; but it is the revolt of the whole body against conditions
affecting a part which constitutes pain.
Amidst the maze of perplexities which lies between physiology and
psychology, there is, however, one fact which stands out clear and bold:
the brain can create nothing. We have seen how matter is taken into the
body and matter is cast off from the body. We have seen how energy is
released in the body from chemical compounds, and made use of by the
body. So now, after a moment’s thought, it must be plain that every
stimulus which goes to the brain must have its effect there, and that a
man’s thoughts and conduct are entirely dependent on what has, at some
time or other, come in from the external world. The association centres
can evolve wonderful thoughts, but they are structurally derived from the
grosser sense organs, and must get all the material they work upon from
them.
The nervous system puts the body into relation with the external world
as a whole, but for convenience it is subdivided into the afferent
system, by which impressions come in, and the efferent system, by which
the muscles are set in motion. Of the two halves, the afferent system
has a just right to priority, for the efferent system is merely its
consequence. Sights, sounds, smells, etc., reach the brain by afferent
paths from the external world, and are there moulded into thoughts. Their
effects we see in poetry, architecture, sculpture, or laundry work,
according to the method of the brain in treating the raw material it
receives, and of a quality corresponding to the fineness with which the
brain examines them, and can control the motor organs of the body.
Whatever goes in at the afferent door, and some people’s sensory
apparatus is much more easily affected than others, produces its effect
within. Sometimes the energy is expended in thought, sometimes in action;
sometimes it trickles away as laughter. But all these phenomena have
a material basis: matter producing changes in matter. ‘Those delicate
tissues wherein the soul transacts its earthly business,’ as Stevenson
so picturesquely describes the brain, stick to their earthly business.
There is no astral department opened yet. A man may evolve a great idea
from the data he receives, but he must give it a material coefficient
if he does not wish it to be lost to his earth-bound brothers. He may
write it in a book, or he may sculpture it in marble; but the most
convenient means of communicating with his fellows is by sound, which he
can command by expelling the air in his lungs over vibrating cords in his
throat. These cords are adjusted at the position and tension to give a
desired note; and the cavities of the chest, throat and mouth acting as
resonators, a noise is produced, which is shaped by the tongue, lips and
teeth into words.
By means of language the human body is enabled to co-operate with others
of its kind for the development of the resources of the earth, the
shaping of society, and the forming of individual character. But here
physiology ends and other sciences begin.
ESSAY V.
THE BODY.
I.
Such, as far as it can be compressed into four short essays, is the
nature of protoplasm. We have sketched out its powers; described how
it exists only in the form of a cell; and shown how cells, by forming
a community and sharing the work, simplify the business of living, and
secure great advantages for themselves individually. But now we have
something fresh—the body.
The body is an organic whole, like the cell. It is composed of cells,
but these cells only develop one of their many powers to its utmost that
they may justify their existence in the community; they do not acquire
fresh properties. So really the body is merely a mass of protoplasm in
which—though in a greater quantity—the same changes are going on that we
find in a single cell. Yet how utterly different is the body from the
cell! what a wide gulf yawns between a man and an amœba!
The body has powers of its own, distinct from those of protoplasm;
and the protoplasm may still be alive when the body it helped to
compose is dead. A few thousand pounds of protoplasm could not have
built Westminster Abbey, but a few hundred men did; for just as out of
protoplasm arises the body, so the body gives rise to the mind, a thing
as much above it as it is above the cell.
So far we have taken the cellular units as our starting-point in
discussing life; but a bird’s-eye view of physiology would be incomplete
which contained no mention of the major tactics of protoplasm—the life of
the body. We must consider the needs of a man as such.
A man requires, as we have described before, air and food. The air must
contain the proper amount of oxygen, and the food must consist of liquids
and solids.
The important liquid is water. More than half by weight of the whole body
is water, and we are always losing it: through the skin, through the
lungs, and through the kidneys. People may drink alcohol with water, but
not instead of it. Indeed, the more alcohol they take, the more water
they require, for if they take their spirits in an undiluted form, they
take water out of the body. If you dip a piece of wet cloth into alcohol
for a minute, it dries with remarkable rapidity, because the water has
been absorbed out of it. In the same way, if you drink neat spirits, they
pass into the blood and stimulate the nervous system, ultimately being
excreted by the kidneys; but on their way through the tissues they absorb
a great deal of water, which must be replaced.
Milk is often spoken of as the ideal food, and so it may be for very
young animals; but it lacks one important constituent—iron. A young
animal is born with enough iron in its body to do without any in its food
until it can take something better than milk. If it is weaned late it
becomes anæmic. An adult animal requires iron and also a certain amount
of solid food. Its alimentary canal is provided with a good deal of
muscle; and this muscle, to be kept healthy, must have something to work
upon—in fact, be exercised.
A man’s food should contain a certain amount of coarse
material—cellulose, for instance, which forms the envelope of vegetable
cells. And here we see a distinctive feature of the body. Protoplasm can
make no use of cellulose, there is no digestive juice which will act upon
it; but its presence in the alimentary canal in the form of husk and
small seeds stimulates the walls by contact, and produces peristaltic
movements.
In Essay II., which dealt with the chemistry of the body, we said that
if we were only to live upon meat we should tax our digestive apparatus
severely by having to eat more proteid than we required in order to
get enough carbon. The converse, however, is equally true: if we fed
only upon vegetables, we should again have to over-eat. Plants most of
them contain large stores of carbohydrate; potatoes and rice are rich
in starch, onions in sugar; but an exclusively vegetarian diet would
necessitate our consuming huge quantities, as its proteid-supply is
bad. It is defective not only in amount—for sometimes, as in beans, the
proportion is fairly large—but in being so indigestible that a good deal
of it passes through the body unabsorbed.
Both science and experience teach that we live most economically upon the
carbohydrates of vegetables and the proteid of animals, and that our food
is the better for being cooked. In cooking, parasitic animals which are
strong enough to survive the ordeal by acid in the stomach are killed,
and the food itself is made more accessible, the indigestible cellulose
envelopes of the vegetable cells being burst open, and the collagen of
the connective tissues converted into gelatin.
No less important than the quality of our food is the quantity; and here,
again, we get a good illustration of the necessity for regarding the body
as a whole. A healthy man’s appetite is his best guide, and if he follows
it he cannot go far wrong. People who arrogate to themselves a wisdom
superior to that of Nature little know the harm they do when they force
food down an unwilling throat. The cells of the alimentary canal digest
and absorb what is sent to them, minding their own business, which is not
to criticise the appetite.
‘Theirs not to question why;
Theirs but to do and die.’
So the digestive and excretory systems embark on hard and profitless
labour, and the whole body suffers.
Passing on to another subject, we find that the body eats that it may
work, and works that it may eat. This cycle comes naturally enough to
animals which have to go and find their food, but men with a sedentary
occupation have, in view of the artificial conditions under which they
live, to take constitutional exercise.
There are many reasons why the numerous and bulky muscles with which
the body is endowed must be constantly used. In the third essay in this
volume we saw that the flow of the lymph and the blood in the veins is
largely dependent upon the movements of the limbs. Muscular exercise,
therefore, must be taken to prevent the circulating streams from growing
sluggish. Obviously, many evils must arise if they do so. Not only would
the muscles be starved by the slowness with which they received their
food, but they would also be poisoned by the slowness with which the
products of their own metabolism were removed. The blood-stream would
become tainted, and the brain, which requires pure blood, would suffer.
In other ways, however, than by their action on the vessels themselves
do the muscles help the circulation. Exercise has secondary effects
upon the circulatory and respiratory centres in the base of the brain,
and makes the heart beat more strongly and the diaphragm contract more
forcibly. The influence of the latter upon the circulation we have
already described; but its vigorous action is required not only to aid
the circulation through the liver and viscera, but to inflate the lungs
to their fullest extent. In the breathing of a man who takes no exercise
only a small part of the air which the lungs hold is pumped out at
each breath, the greater part remaining stagnant in chambers which are
practically unused. Thus, not only is the revenue of oxygen diminished,
but there are numerous little crannies in the body filled with still,
warm air which are ideal nurseries for bacteria. The devil of consumption
does not allow such dwellings to long remain swept and garnished.
Without exercise the sweat glands of the skin will not act, and its pores
get closed up. The muscular coats of the alimentary canal, too, reflect
in their state of health the condition of the voluntary muscles; laziness
is followed by constipation, for if the voluntary muscles rust, so do the
involuntary.
The muscles, moreover, must be well developed and kept in a healthy
condition for their own sake. They form a large part of the whole bulk,
and no healthy man can have unhealthy muscles. Ignorant people sneeringly
say that they have no ambition to lift weights or bend pokers; but
they should remember that they are dependent upon their muscles for
their bodily warmth, and also to save their internal organs from being
oppressed by their own weight.
The bones of the skeleton do not rest one upon another; they are jointed,
and kept slung in position by springing bands of muscle attached to their
levers. If these muscles are not properly developed, they tire under
the strain of holding the frame up, and a disastrous rearrangement of
the organs is made to save labour. The chest is drawn in, the hips and
knees thrust forward, and the man stands with cramped chest, compressed
viscera, and his diaphragm under dire constraint. The result of the
redistribution of weight is that his bones tend to rest upon one another
like a column of bricks, and his whole weight is upon his heels. Such an
individual cannot walk; he stumps along, jarring his whole body at every
step.
A pleasant contrast is the athlete. The athlete is a man who endeavours
to develop the latent powers of his body to the utmost; and in the
achievement of this desirable object the physiologist takes great
interest. Physiology has revolutionized our ideas of training, as well
as many other things, during the last half-century. We now recognise
two kinds of training—the preparation which a healthy man makes for an
occasion on which unusual exertions will be expected of him, and the
slower and permanent strengthening of the whole body, now usually called
physical culture. The former is a comparatively short process now that
athletes no longer think it _de rigueur_ to live in bestial intemperance
when they have no contest in immediate prospect. A little extra exercise,
to stimulate excretion and clear away any waste products that may have
accumulated in the tissues; a little extra proteid in the diet, since
there is at first a slight inclination to growth; a good deal of extra
carbohydrate, since the muscles want extra fuel; rest—and the man is
ready. Many athletes live continually in training, and are ready at any
moment to ‘fight for their lives.’