introducing to view the doubled or convoluted form occasioned by the
folding of the material in a series of windings,--a form which is in
complete contrast from the smooth surface characteristic of the brain in
all lower orders. This series of windings or convolutions appears quite
decidedly in the brain of the _cat_, in a manner very similar in the
brain of the _dog_, and with still greater beauty and amplitude of fold
in the brain of the _horse_. This folding process which is resorted to
in the case of all the higher quadrupeds, seems a contrivance by which
it is possible to pack a greater amount of material in such a way as to
expose a greater degree of surface, within the narrow space at command
inside the cranium. In all the three examples named, great prominence
is given to the bulbs of smell, which are spread out quite conspicuously
in front of the brain,--implying, as in lower examples, a life largely
governed by sense of smell.
[Illustration: BRAIN OF HORSE, WITH BULB OF SMELL IN FRONT, LITTLE BRAIN
IN REAR.]
[Illustration: DIAGRAM OF SENSORY AND MOTOR APPARATUS. THE UPPER IS THE
SENSORY, WITH BULB, NERVE LINE, AND NERVE CELL. THE UNDER IS THE MOTOR,
WITH MUSCLE, NERVE LINE, AND NERVE CELL.]
Omitting special reference to animals of great bulk, and possessing
enormous muscular power, such as the elephant and the whale, both of
which have singularly complicated and beautiful brains, I pass to the
races of _monkeys_ and _apes_, which are nearest in structure to man. In
these animals the configuration of body is certainly the nearest
approach to the human figure which is to be found anywhere in the animal
kingdom. They can not, indeed, assume the perfectly erect posture of
man, but they come very near to it; and though they move on all four
limbs, feeling themselves more secure in that mode of advance, they have
a formation of hand analogous to that of man, with a distinctly formed
thumb, enabling them to grasp an object in a manner closely resembling
the human grasp. The apes have even an advantage over the human race,
for they have a thumb on the foot, as well as on the hand; which may
also have its own disadvantages, for it might prove no convenience to us
if we were so endowed. But the presence of the thumb on the lower
extremities suggests the use which it serves in the animal's ordinary
life, in grasping the branches along which it moves. If from the
similarity of outward configuration, we pass to contemplate the brain,
we find here also great similarity of structure. And indeed if the
relations of muscle, nerve, and brain be as already indicated, it
follows from the resemblances of outward form that there must be a
greater resemblance between the brain of man and the brain of the monkey
and of the ape, than between the human brain and that of any other
animal known to us. And so it proves to be. The brain of the monkey has
its subdivisions and convolutions very similar to those of the human
brain, only the convolutions are simpler in arrangement. In outline it
is deficient only in the diminished bulk of the front part, and also the
back part of the organ; but in its expansion it resembles the human
brain in this, that to the rear it spreads back over the cerebellum, so
as to cover it. The brain of the ape, including under this designation
the orang, gorilla, and chimpanzee, is in still closer resemblance to
the human, being still, however, somewhat simpler in the arrangement
of its convolutions, but so closely approximating that the exact state
of the case is as nearly as possible described, if we say that the brain
of the ape, while it is decidedly smaller, appears like a miniature of
the human brain in a slightly undeveloped state.[CV]
[Illustration: HUMAN BRAIN]
[Illustration: BRAIN OF MONKEY, WITH CEREBELLUM BENEATH]
The human brain is an elaborate organ, exceedingly complicated in its
convolutions. We can not, indeed, describe it as the most convoluted,
for the brain of the elephant is at least as distinguished for the
beauty and complication of its folding, and the brain of the whale is
far more minute and detailed, presenting quite a multitude of minute
convolutions. For descriptive purposes, the human brain is divided into
four superficial areas, known as lobes, and pretty clearly defined by
certain natural boundaries. From the lower part of the organ, entering
at a point scarcely half way back is a fissure or cutting running up
into the mass in a direction uniformly inclining towards the rear, known
as the Sylvian fissure; while coming over the summit, at a point near
the middle, and inclining down towards that just described, is another
fissure, known as the fissure of Rolando. By these two deeply cut
hollows, the brain is marked off into four separate areas superficially,
a front and a rear lobe; and two central lobes, the one upper and the
other under. Besides this there is a concealed and isolated lobe,
described on account of its situation as an island, which is covered
from view by the overlapping of the two sides of the Sylvian fissure.
Such is a description in outline of the configuration of the human
brain, to which must be added the statement that each lobe is filled in
with its own special arrangement of convolutions, each one having at
least three well defined lines of convolution. Each of the hemispheres
is similarly arranged, though not by any means quite identical in
disposal of convolutions, yet the general description now given is
strictly applicable to both. The two hemispheres, connected mainly with
the ramification of nerve fibre running to the opposite sides of the
body, are united together a considerable way down by a transverse band
of nerve fibres, which at once unite the two into one organ, and make
the union so effected a living efficient union by carrying a multitude
of lines of communication from the one side to the other. Just below
this, in the interior of the organ are two great central bodies, known
as the basal ganglia, and consisting of nerve fibres massed together
with grey matter around them, that in front being chiefly motor nerves
brought to a junction, the latter sensory nerves combined in like
manner. The same arrangement holds in both hemispheres, thereby
providing that the respective masses of motor, and of sensory nerves lie
exactly opposite each other. Behind these in the centre, lying in a
position under both hemispheres are four small bulbs connected with the
nerves of vision, and also with the cerebellum; and behind them, covered
by the posterior lobe of the brain is the cerebellum itself, or little
brain, largely concerned with coördination of movements, or equilibrium
of the two sides of the system. Just below these arrangements the two
great cords of nerve fibre descend towards the body, which are covered
by a transverse mass, known as the bridge, appearing complete as a
crossing, and containing transverse fibres from the cerebellum, as well
as a series of longitudinal fibres. Immediately underneath the bridge
are pillars or masses of nerve, constituting the crowning portion of
the spinal system, and formed in eight distinct bodies, the two in front
and the two in rear being elongated and known as pyramids, those in the
centre being rounded in figure. From the elongated bodies, the nerve
fibres pass across to the opposite sides of the body. This gathering is
known as the _medulla oblongata._ Just beneath comes the spinal canal,
from which at the different joints of the spine are given out a suitable
supply of sensory and motor nerves as previously described.
Having thus given a general account of the central arrangements of the
nerve system of the human body, it is important to state that an order
of things closely analogous obtains in other and lower orders of
organism, in respect of interior plan, so that if the interior of the
brain of the dog were laid open to view it would present a plan of
distribution very similar to that now described.
To complete the view of the functions of the brain as indicated by
recent research, I have next to give a brief account of an extended
course of experiments of great delicacy designed to ascertain whether it
may be possible to localize certain functions within a definite area of
the brain. All are familiar with the fanciful subdivisions of the outer
surface of the human skull, under the name of phrenology, represented on
moulds of the head, all marked with dividing lines and figures. This
pretentious and unscientific assumption of knowledge which no one
possessed, has had its time of popularity, aided by a general
recognition of comparative superiority in head formation in persons of
known ability. Any thing equivalent to an exact partition of the bony
covering protecting the brain, has not been favored by scientific
observations; but these fanciful maps of the head, which have been sold
cheap, and fully certified, may serve as a guide to a general notion of
what has been attempted on the surface of the brain itself, after
removal of the skull. The illustrative aid, however, consists in nothing
more than the suggestion of distinct areas, for there is no analogy
between what has been discovered by the observations now to be
described, and the "bumps" alleged to be found on the cranium.
The conjecture which may be said to have originated experiments as to
localization was that there was a close resemblance between the action
of nerve energy, and an electric current. The attempt made was to
similate the action of the nerve cells, by discharging a current of
electricity upon the grey matter of the brain, and recording the results
which came under observation. Experiments were begun in 1870 in Germany
by Fritsch and Hitzig, the dog being the animal experimented upon. The
investigation was undertaken also by Dr. Ferrier of King's College
London, and much more extended and varied results were published by him
in 1873. Confirmatory work, executed with many precautions, was
undertaken on the subject in 1874 by a committee of the New York Society
of Neurology and Electrology,--a committee which included Drs. Dalton,
Arnold, Beard, Flint, and Masson,--testing results by frequent renewal
of the experiments; and at the same time, a similar course of inquiry
was being conducted in Paris by Carville and Duret.[CW]
By these investigations, the possibility of electric stimulation of the
cortical or grey matter of the brain, and consequent activity of the
nerve system has been fully established; and though there is still
considerable diversity of opinion concerning the interpretation of the
facts, it can not be disputed that by directing the electrode on certain
well defined areas of the surface of the brain, it is possible to bring
into natural activity certain portions of the muscular system, as
controlled by the motor nerves.
The plan adopted is, after putting the animal into an insensible state
by use of chloroform, and removing the cranium so as to expose the
brain, to apply the electrode connected with an electric battery to a
given point on the surface, record the result, and gradually shift the
needle round the original spot until a new result is obtained, in which
the spot previously tested becomes an index for the boundary of one
circle, and this marks the fact that a new circle has been entered.
By this process of investigation a series of centres for active
stimulation have been discovered. These number, in the brain of the rat,
six; in the brain of the rabbit, seven; of the cat, eleven; of the dog,
thirteen; and of the monkey, at least, seventeen. A curious limitation
to the area of experiment has been encountered here, for all the centres
identified are found to cluster over the central region of the brain,
and both the front and rear parts of the organ are silent, offering no
response however greatly stimulated. The explanation of this silence
remains a matter of doubt. It may be that these portions of the brain
are concerned with movements which do not come under the observation of
the operator, or that they are centres of sensibility from which no
movement can naturally follow, or that they fulfil functions which can
not be recognized by this mode of experiment. Uncertainty hangs over
this department in the investigation.
The actual results may be indicated by a few examples. At a point well
forward in the brain of the dog, marked number one by Ferrier, is a
centre which when stimulated leads to movement of the hind leg on the
opposite side; and by exciting another portion of the brain quite
contiguous, marked number four, movement of the opposite fore leg is
produced. By exciting a point situated over these two and on a distinct
convolution, wagging of the tail is induced. By transferring the needle
to a point much lower down, towards the base of the brain, but still
well forward, marked by Ferrier nine, the mouth is opened and the tongue
moved, while in many cases a decided bark is emitted. These examples
may suffice to indicate the class of results obtained; and similar
results have been seen in all animals subjected to this test, with such
variations as may be considered inevitable in view of the configuration
of the animal.
While distinct areas or circles of the brain have thus been marked,
warranting localizing of certain functions, the facts connected with
these experiments do not favor the view that each area is to be taken as
so rigidly distinct that it may be supposed to operate separately in a
quite isolated manner. On the contrary, a conjoint action of several
centres seems more commonly implied when the natural activity of the
brain is contemplated in line of these results. Additional weight must
be given to this consideration, when it is noticed that the centres are
nominally _motor centres_,--movement and not sensibility being the
result most patent to the observer,--nevertheless on closer scrutiny it
proves true, that many of the movements occasioned by electric
stimulation are those induced naturally as the result of sensation. Such
for example are the movements of the eyelids consequent upon a dazzling
of the eyes, or movement of the ears because of a startling sound. In
this way it becomes clear that within a given area a centre of
sensibility is in communication with a motor centre close by, or it may
be even at some little distance. Thus this most delicate and difficult
course of investigation supports the view that much of the activity of
the animal organism is provided for by an established connection between
nerve cells respectively presenting the terminus in the brain for a
sensory nerve, and the starting point for a motor nerve, or point of
communication with such a nerve. From this conclusion, it follows that a
very large amount of the activity which we witness in the case of
animals, often attributed to instinct, or even to voluntary
determination, is to be described as _sensori-motor activity_. That is
to say, the action is brought about by a contrivance which may be
described as partly mechanical, partly chemical. Its history may be
sketched in this way: an impression is made on one of the nerves of
sensibility, or on one of the organs of special sense, such as the eye
or ear; a wave of impulse passes along the incarrying nerve fibre,
leading to molecular change in the nerve cell, and to sensibility in
some way unknown; the excitation occasioned there is extended along a
connecting fibre to a second nerve cell, which is the starting point for
a motor nerve; along that line the impulse is instantly and inevitably
continued; and as an almost instantaneous result, without any form of
sensibility to indicate what is taking place, the muscular energy is
liberated, and action is the direct consequence. The problem which
immediately arises is this,--How far may the activity of all living
organism be accounted for in this way, including even the activity of
man? This is a problem which will present an interesting subject for
discussion in the next stage of this inquiry, the import of which must
now be made apparent by the sketch of the structure of the nerve system,
and the results of the experiments as to localization.
Nothing more is now required to complete this narrative leading up to
this problem, and discovering its proportions, than a brief account of
correlative inquiry which has afforded strong confirmatory evidence as
to the truth of the conclusions favoring localization, and coördinate
action of different portions of the brain as the central organ governing
the whole nerve system. The corroborative evidence at once supporting
the conclusions as to localization and favoring their extension to human
nature is obtained by reference to the results of injury to the nerve
system at various parts of the body, and injury to the brain as
ascertained after death. Continuing experiments on the animals, it has
been shown that even if a portion of the brain be cut away, it is still
possible to operate on the nerve lines in the usual manner by means of
electricity. Pushing experiment in this direction still further it has
been found that more serious injury permanently destroys the centre, and
entails paralysis of the muscles controlled by it when in a healthy
state. In like manner it has been proved that if the nerve itself be
cut, the communication is at an end, and movement by stimulation has
become impossible.
By perpetually occurring cases of paralysis in human experience, and
careful examination after death of the exact situation and extent of
disease in the brain, it has been shown by accumulation of evidence,
that the laws which provide for sensibility and for muscular activity in
the history of the lower animals, do also hold in the case of man. While
the brain continues in full vigor, all the usual forms of sensibility,
and modes of action are simple; where these have become disturbed,
restricted or impossible, some injury has been accidentally inflicted on
the brain of the sufferer, or disease has begun in the organ, and has
gained a hold exactly proportionate to the forms of restraint and
disturbance which have become outwardly manifest. These are results
which show how much is due by way of sympathy, and patience, and
encouragement to those who suffer under any degree of brain injury or
disease, due from all around them whose conduct may have any part in
determining their experience. These results testify how closely the
human organism stands allied to lower orders of organism around; how
many homologies of structure there are, and how many analogies in
experience. These things declare that science has a clear and
unchallengeable field of inquiry in seeking an explanation of human
nature on the same lines of procedure as those which have been followed
in ascending the scale of living organism. The nature and extent of
materials at its disposal as the result of the most recent
investigations have now been indicated. The problem is, How far can the
anatomy and physiology of the human frame account for the facts of human
life? The strength and practical power of religious thought in the world
will depend upon the answer, for science must here carry some test of
religion. On the other hand, the problem which human life presents is by
far the most severe test which science has to encounter. In facing the
facts, science is engaged with the settlement of its own
boundaries,--the demonstration of its own limits. In facing this highest
problem which human observation encounters,--man's explanation of
himself,--let us cease from comparisons between scientific claims and
religious, and let us face with patience and resolution the
question--What is the exact place, and what the destiny of man, who has
piled up the sciences, and midst the turmoil and conflict of life, has
found his most elevating exercise, and most profound calm, in worship of
"the King eternal, immortal, invisible, the only wise God"?
FOOTNOTES:
[CS] Protoplasm, see Appendix VII.
[CT] Unless references are otherwise given, illustration of the
structure of brain here referred to, will be found in my work, _The
Relations of Mind and Brain_, from p. 125, onwards.
[CU] _The Brain as the Organ of Mind_, by Dr. Bastian, p. 115.
[CV] See Appendix XI.
[CW] For detailed narrative, see my work on _The Relations of Mind and
Brain_, chap. iv. p. 79.
LECTURE VII.
MAN'S PLACE IN THE WORLD.
The accumulated interest gathered around the direct and collateral
investigations bearing on the development of species, has naturally
turned greatly increased attention on man's position in the universe. As
has been shown by study of the nervous system belonging to animal life,
all organism has been constructed on a uniform plan, advancing in
complication as the organism becomes more intricate in structure, having
separate parts assigned to distinct functions. This uniform plan is seen
to culminate in man. Thus it follows, that man appears to the scientific
observer, as the last or most advanced figure in a gradually ascending
scale. That this is man's place in the field of organized existence no
one will doubt.