_THE BRAIN_
I
An animal deprived of the brain is a machine which requires external
stimuli in order to move. An uninjured animal is also a machine, but it
differs from the other by that power in itself which renders it capable
of moving and acting.
When an animal with its brain removed is touched on any point of its
body quite lightly, it does not respond at once to this external
stimulus, and only when these light touches are often repeated is a
reactionary movement excited. There are some very wonderful experiments
which made a great impression on me, when I first saw them performed
by my friends Kronecker and Stirling in the laboratory in Leipzig.
They took a decapitated frog, and fastened between the toes of one
of the hind-legs a pen, which made marks on the paper of a rotating
cylinder whenever the frog moved. Between the toes of the other leg
they fastened the wires of an electric current; a pendulum alternately
opening and closing the current in such a manner that an interrupted
stimulus was obtained. It was strange to see how the headless frog
responded regularly for hours. When stimulated by a weak current
(so weak that it could not be felt on the tongue) more numerous
repetitions, perhaps thirty, were necessary before the frog responded
by a spasmodic movement. If the stimulus were stronger a much smaller
number was sufficient to cause reaction, and this continued until life
was extinct.
Stimuli accumulate in the spinal cord. We all know it from experience;
when we have something in the throat which tickles us, the slight, and
at first scarcely perceptible, irritation becomes almost unbearable
if it continues, compelling us to cough in order to remove it. As
the Italian proverb says, one cannot disguise a cough. Even a slight
tickling of the skin has the same effect, and in the functions of
reproduction the repetition of slight stimuli produce greater and more
ungovernable reflex movements.
There are, however, impressions which remain longer accumulated in
the brain before their energy finds expression in muscular activity.
Sometimes a part of the nervous system charges itself slowly, like a
Leyden jar under the influence of weak electric sparks, the tension
of the nerve-cells remaining, as it were, hidden, until suddenly
discharged by a contact or some very slight impression. We are
astonished; it seems an accidental explosion to us, an effect out of
all proportion to the momentary cause, forgetting that fire glows under
ashes, that the force had been slowly accumulating, and so we believe
we have accomplished the act by means of the will.
The aptitude of the nerve-cells to accumulate and preserve external
impressions is such a leading fact in physiology that I do not know any
more important one.
If I were asked the difference between the brain and the spinal cord, I
should say that the brain is more capable of accumulating impressions,
not because of the difference of its substance, but because in it the
nerve-cells serving this purpose are found in greater abundance.
The manner in which the brain has formed itself in the evolution of the
animal world will render the comprehension of its activities easier.
Let us consider the simplest creatures, those possessing, so to speak,
only a spinal cord. The nerves branching off from the upper part to
the nostrils, eyes, ears, mouth, and elsewhere, were subjected during
the long series of generations to more continuous stimuli than other
nerves. The cells placed at the roots of these nerves were constantly
excited by impressions from the external world; chemical processes and
combustion would be more rapid in them, hence the necessity of a more
copious flow of blood to those parts which were in greater activity.
These cells multiplied rapidly at the roots of the organs of sense,
gradually covering a wider field. As the animal structure became more
perfect during evolution, and the relations of the animal to the outer
world increased, the more abundant and active the cells at the roots of
these nerves would become. We must not think here of one individual,
although individual exercise does strengthen an organ, but must fix
our eyes on the interminable chain of generations, all working in this
direction.
It was heredity (by which we still transmit to our children the
structure and functions acquired by the nerve-centres) which, through
the incessant efforts of our progenitors, enlarged this fertile field,
until at last it resulted in the mass of the brain.
If, on visiting a museum of comparative anatomy, the reader will look
into the glass cases set apart for the study of the nervous system, he
will see that the lowest animals have only a spinal cord, or a very
small protuberance at the place corresponding to the brain. As the
animal structure becomes more complicated, there is a visible increase
of the protuberance, which enlarges gradually the nearer one approaches
the superior animals, until at last it reaches its maximum size in man.
II
One of the greatest experimenters of modern physiology, Flourens, had
already given it as his opinion that the whole cerebral mass performs
the same functions in all its parts, and that if one portion be taken
away, those contiguous to it charge themselves with its offices. This
affords a partial explanation of the fact that wounds of the brain are
far less dangerous than those of the spinal cord. It is always a great
wonder, even to us physiologists, every time we convince ourselves on
living subjects that the brain is without feeling. Men have been seen
who suffered great portions of their brain, which protruded from the
skull, to be cut away, and sick drunkards or madmen, who, through the
wounds in their head, seized hold of the brain with their hands and
destroyed it.
Only in the last few years have physiologists succeeded in preserving
alive for some time dogs of which nearly all the convolutions of the
brain had been removed. Professor Goltz brought a dog in this state
from Strasburg to London, in order to show the phenomena which an
animal then presents, at the International Congress of Medicine. I
extract a few fragments from Professor Goltz’s work,[9] in order to
give an idea of the phenomena exhibited by dogs when deprived of a
great part of their brain.
[9] F. Goltz: _Ueber die Verrichtungen des Grosshirns_, p. 61, and
following. Bonn, 1881.
A brainless dog has a stupid, inane look. One reads idiocy even in
his eyes. His movements are slow and uncertain. It seems as though he
needed far more time than usual to come to a decision. His gait is like
that of a goose, there is something inexpressibly strange and comical
in it. The animal always walks straight on like an automaton. If he
meets another dog, he steps over him if he is little; if he is big
he may lift him with his head, or knock him down, but on he goes. He
tries awkwardly to step over every object he meets, although by simply
stepping aside he might pass on without hindrance. He only finds his
dish of food with difficulty, smell guiding him better than sight; he
snaps stupidly at everything he sees, even biting his own paws till he
howls with pain. He can no longer find the fragments of bone that fall
out of his mouth while chewing.
Dogs like these are no longer capable of learning anything, and one
might almost say that they have forgotten what they already knew; for
instance, they no longer give their paw to their master, as they used
to do. Their whole intellectual life is extinguished; only when they
hear a knock at the door do they bark, but they always begin too late.
Two dogs that hated each other, bit each other when they met, even
after both had lost a great part of their brain. Memory diminishes
in proportion as larger quantities of the brain are removed, and
disappears wholly when nearly the whole organ is wanting.
III
In order better to understand the working of the brain, we may divide
it in imagination into two parts: a lower, situated at the base of the
cerebral hemispheres, which forms the direct continuation of the spinal
cord and is the centre of those movements which arise involuntarily
during emotion; and another part in the upper story, as it were, which
consists of the cerebral convolutions, is also in connection with the
spinal cord, and must be considered as the seat of voluntary movement.
The enormous difference between the mind of a man and that of a child
exists because in the latter the upper story of the brain is not
developed, the convolutions are scarcely indicated, the organs of
will and speech are wanting. As the large pyramidal cells appear and
increase, the child acquires intelligence and speech; connections are
established with the lower story in order to set muscles and organs
which were before inactive into movement. But the difference between
these two stories of nerve-centres continues during the whole life. I
shall explain this by a few examples. A man is paralysed in consequence
of some injury which prevents the upper story of his brain from
communicating with the spinal cord. Hands and arms no longer move under
the influence of the will, but when some long-expected person appears,
or some sudden shock is given to the emotional sphere, he will be able
to lift his arms. There is a paralysis of the facial nerve in which
the voluntary closing of the eye is impossible, but if anyone makes a
movement, as though he were going to poke his finger into the eye, the
lid closes instantly. Later, we shall instance men who have remained
dumb for a long time, and have regained their speech in consequence of
a fright.
Dogs deprived of a large part of the upper story of the brain make no
sign of recognition when they see themselves threatened by the whip,
but if it is cracked they scamper off hurriedly, or rush forward at
it. A mouse with its hemispheres and optic thalami removed remained
undisturbed by every noise but that resembling an approaching cat, when
it jumped and fled.
By means of injuries to the brain physiologists can easily check the
activity of certain voluntary movements. If the peduncles of the
cerebellum and certain points of the cerebrum are injured, dogs can
be made to go either only to the right, or to the left, continually
backwards, or in a circle, as though they were in a circus. The will
of the animal is still in existence, but all his efforts are, as often
with us, fruitless. In spite of himself his body is drawn in the
direction determined by the lesion of the nerve-centres. Claude Bernard
tells of a brave old general who, by a cruel irony of fate, could only
march backwards.
Many physiologists have of late years tried to establish with precision
the point of the brain which is the seat of emotional expressions; that
is, that part, the destruction of which obliterates every expression
of fear or pain in the animal, although allowing life to continue. One
of the latest works published concerning this is by Bechterew. His
observations show that a dog, in whose brain the corpora bigemina and
quadrigemina have been destroyed, still barks and shows his teeth
if anything loathsome is given him to eat, or if something smelling
disagreeably is put before him; but that he is bereft of all expression
of disgust and loathing after the two optic thalami have been removed.
Hence Bechterew concludes that the paths of transmission along which
pass the involuntary commands which cause the muscles to contract, in
order to express the emotions, concentrate in the optic thalamus, which
is one of the deepest parts of the brain. The upper story of volition
and the lower of the emotions have here their point of union, whence to
excite in the muscles of the organism all the characteristic movements
of the passions.
IV
Let us now see what instinctive qualities we inherit from our
forefathers, and what others we acquire through our own experience.
Long ago Galen performed a very simple and instructive experiment. He
cut a kid out of the body of its mother, laid it immediately on the
ground, and, near its head, dishes in which were oil, wine, honey,
vinegar, water, and milk. He then stood to observe the first movements
of the animal. After trembling a little, the kid got up, scratched
itself, smelt a few of the dishes, and at last drank the milk.
There are birds which, scarcely out of the shell, catch flies with such
precision that one is astonished at their bringing with them skill such
as must usually be acquired by long practice. Certain butterflies, on
leaving the cocoon, fly at once into the air, directing their flight
with the most perfect accuracy towards the flowers, to suck the nectar
from their cups.
We shall return to this point when we investigate fear in children.
Let us here only state that, at his birth, man is far less perfect
than many animals. He must acquire by education and experience much
knowledge of which animals are possessed at the beginning.
The less care parents give to their young, the more completely do they
furnish them through heredity with instinctive knowledge; the less
considerable this inheritance, the more care and attention must parents
give to their offspring in order to keep them alive.
This apparent inferiority in the gifts of instinct at birth is, as it
is with the gifts of fortune, fully compensated for by the greater
capability of those animals to increase their intellectual capacity by
education, and by the work of their own experience to surpass by far
animals more favoured by instinct; so it is with man, who subjugates
them all.
Let us think of the tremendous difficulties which walking presents to
man. Children are at first very much afraid of falling, even before
they have experienced such a thing. Every movement is performed with
difficulty; it is at first a task painfully learnt; gradually it
becomes less a matter of reflection, until at last one can scarcely
call it voluntary. We may not call it automatic, because when the will
to make us walk is wanting we do not move, but when we have once set
out on a walk, or to make a journey, we may go on for a long time
without reflecting in the least that we are walking.
Ribot[10] tells of a violoncellist who suffered from epileptic vertigo,
during which he became unconscious. He earned his living by playing in
the orchestra of a theatre, and it was often noticed that he continued
playing in time, even after he had lost consciousness. It has happened
to all of us to read aloud without understanding what we have read,
or absent-mindedly to write one word for another, and many will have
experienced such extreme fatigue that they have slept while walking.
There are endless phenomena proving that movements which at first
cost a great effort of the will, become at length so habitual that we
perform them without being aware of it.
[10] Th. Ribot: _Les Maladies de la Mémoire_, p. 9. Paris, 1881.
Now what is the cause of this transformation of voluntary into
automatic movements?
When we first try to execute a series of complicated movements the
brain must work hard. If the cells of the upper story--that is, of
the convolutions--do not take part in it, it all comes to nothing;
the assistance of all the organs of sense is necessary in order to
shed light on the confusion of orders and counterorders which must
be sent to all the fibres of the muscles. The work is accomplished
under the direction of a competent, enlightened administration; but
through repetition of the same work, easier paths, broader lines of
communication are formed in the lower story of the brain, and gradually
the same work can be performed by the cells of the lower part--that is,
without the co-operation of the will. This is easy to understand. The
oftener a thing is repeated, the more the mechanism tends to become
permanent, and it ends in the work being despatched by the less noble
parts of the brain.
The serious aspect of the question is, that physiologists would like to
catalogue many qualities which we have always considered as the most
noble of our character, the most sublime feelings of human nature,
amongst the automatic movements and more material instincts in the
lower story of the brain.
For instance, for the maintenance of our species the love of the mother
for her children is indispensable. The lower animals that produce a
numerous offspring may carelessly abandon them, but when the progeny is
sparse, there is no other way to preserve the species than through the
greater and more prolonged attention on the part of the parents.
Let us for a moment study the character of the monkey. I quote from the
celebrated book by Brehm, who conscientiously relates what he himself
noticed.
'When the monkey-suckling is unable to do anything for itself, the
mother is all the more gentle and tender with it. She occupies herself
with it unceasingly, sometimes licking it, sometimes running after it
or embracing it, looking at it as though revelling in the sight of it;
then she lays it against her breast and rocks it to sleep. When the
little monkey grows bigger the mother grants him a little freedom, but
she never loses sight of him; she follows his every step and does not
permit him to do everything he likes. She washes him in the brooks and
smooths his fur with loving care.
'At the least danger she rushes to him with a cry, warning him to take
refuge in her arms. Any disobedience is punished with pinches or cuffs,
but this seldom happens, for the monkey does not do what its mother
objects to. The death of the young one is, in many cases, followed by
that of the mother from grief.[11] After a fight monkeys generally
leave their wounded on the field; only the mothers defend their young
against every enemy, however formidable. At first the mother tries
to escape with the young one, but if she falls, she emits a loud cry
of pain and remains still, in a threatening attitude, with wide-open
mouth, gnashing her teeth, and menacing the enemy with outstretched
arms.’
[11] Brehm: _Thierleben_, p. 49. Leipzig, 1883.
Davancel tells of the profound emotion he experienced after having
killed a monkey. 'The poor animal had a young one with her, and the
bullet hit her in the region of the heart. She made a last effort,
placed the young one on the branch of a tree and then fell down
dead. I have never felt,’ he says, 'greater remorse at having
killed a creature, which, even in dying, showed feeling so worthy of
admiration.’[12]
Whether this is instinct or affection, whether there is any difference
between the love of man and of the monkey, I do not feel called upon
to decide. I acknowledge that it is necessary for the maintenance of
the species that things should be thus, nor need our admiration for
mechanisms made in this way suffer any diminution.
I do not think I deserve praise for loving my mother. I remember what
she did for me; and even if all our affection were only a simple
automatic correspondence of instincts, if I knew that neither had the
power to act otherwise, I should be just as glad to be constituted in
such a manner that I cannot repress the throbbings of my heart whenever
her face rises in my memory. I do not think that my tears and sorrow
show less of love on that account.
And if I still feel myself drawn to the grave of the mother who died
long years ago, thus cherishing her memory by visiting it in the
greatest joys and sorrows of my life, I am glad to be an automaton
feeling the religion of love in this renewal of the grief and tears of
the last farewell.
[12] Brehm: _Thierleben_, p. 106. Leipzig, 1883.