Part 13

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.

The prevailing view of our nature, however, recognizes more in it than bone, muscle, nerve, and cellular tissue, while observational science is capable of recognizing no more than these, so that, if there be any thing more, it is quite beyond the range of physical science, and within the territory of mental philosophy. Here then, is preparation for conflict, which may be accepted as inevitable, because of the advance of science. The occasion for this expectation should, however, be fully understood. Its certainty may be maintained on two obvious grounds. The first is concerned with the history of scientific progress. Science is pushing its way up the extended scale of existence with no exact knowledge of its own limits; knowing what its achievements have been, animated to a high degree by the vastness of the problems still before it, but knowing nothing quite definite as to its own boundaries. The aggressive force of science at such a stage must be great. On the other hand, there is a large body of settled conviction, which has swayed men and moulded society in all ages, which is an opposing force operating on that very line along which science is advancing, and which must be encountered whenever man's place in the universe becomes the subject of inquiry. This opposing conviction is not necessarily religious in type, though it is supported by the whole range of thought concerned with the supernatural. The conviction here referred to, as lying more obviously across the path on which science is travelling, is that concerned with the personality of man, with the rights and responsibilities of individuals, implying accepted conclusions on which the government, and police, and administration of affairs in every nation are based. It must, then, be clearly recognized that the conflict anticipated as inevitable is the conflict of knowledge of one order, with knowledge of a different order. It is conflict of knowledge obtained by the slow and difficult processes available to science, with knowledge possessed by all, applied in the regulation of individual and social life, and systematized in the annals of mental philosophy; or, we may more nearly describe the condition of matters by saying that the occasion of conflict is the determination of science to include all within its own area, rather than the possession of actual knowledge as to the highest order of life, for science is only seeking, and can not profess to have found, an explanation of the functions of human life, as it can profess to have done in the case of lower orders. There could, therefore, be no more mistaken representation of the pending conflict than the allegation that it is a conflict of knowledge with ignorance. To put it in the best light for science, it is the conflict of one kind of knowledge with another; but there is a nearer approach to accuracy if we say that the conflict is occasioned by the _want of verified conclusions_ within the boundaries of science itself, in contrast with very definite conclusions belonging to men generally, and verified by practical tests which scientific men can not refuse. It is not essential to the point, but may be of consequence in view of the range of application belonging to this inquiry, to remark that religious thought is not itself directly involved here; nevertheless, religious thought is deeply concerned in the issue of the conflict.

Having thus briefly indicated the occasion of the conflict, and the contending forces, it is desirable to find the standpoint of science. The nature and origin of life having been passed as problems for which no solution has yet been found, science has concentrated on the functions of the various portions of each organism, and on the contrivances for its protection and continuance in the world; and still more in advance, on the laws favoring the development of species. From outward form it has passed to inward structure, and pressing still more closely towards the secrets of life has endeavored to ascertain by microscopic investigation what provision has been made for maintaining the vital processes involved in the action of organism. Travelling up the advancing orders of animate existence, science has discovered a uniform plan adapted to varying complexity of structure. Thus entered and far advanced on the course of investigation, science sees no limit to its field of inquiry save the limits of organism itself. What has already been achieved, gives full warrant for the claim of inclusion, in which all scientific men naturally concur, and with which men generally will readily agree. This agreement, however, lies on the very boundary line of disagreement and dissension. Immediately when an attempt is made to set forth what is implied, it becomes clear that some scientific men include very large expectations as to what science is yet to accomplish, while others, showing more of the caution of the scientific spirit, decline to commit themselves to dogmatic assertions. Up to the line of agreement indicated we are dealing with science; beyond that line, where we come upon disagreements, we are not dealing with science, but with the comparative sanguineness or caution of scientific men.

What we have before us as clearly admitted on all sides is that human life presents the common characteristics of organic life, and is subjected to the ordinary laws of organism. The problem with which we have now to deal in view of this admission is this,--How far do the functions of organism account for the universally recognized characteristics of human life?

In facing this problem there are not a few scientific inquirers who look upon the mere raising of it as a claim to include all that belongs to human nature within the realm of physical science. They have allowed themselves to regard the two things as interchangeable, and all their researches are in their view so involved in this identification, that they resent the challenging of it, as if it implied antagonism to science. But the scientific inconsistency of this is easily shown. That science must extend its investigations to human organism, admits of no doubt; that by means of this investigation all the phenomena of human life will be traced to organism, is the very thing to be proved, and until established on clear and full evidence is not to be regarded otherwise than problematic. If we are in this matter to be influenced by regard to the slow and difficult procedure in cases of much greater simplicity, we shall be guarded in the utterance of expectations; if we make account of the enormous difficulties to be encountered in arranging the facts to be explained, we shall be still more guarded; and if we remember that the practical demands of life must all be met day by day without waiting for science as an aid, it will not appear strange that the non-scientific thinker regards the whole scientific investigation as wide of the sphere in which questions of self-government are settled, even though this view seems to affirm, without knowledge of both sides, that there is a sphere belonging to human life into which science can not enter.

Still, it must be allowed that in the pathway of science nothing is to be foreclosed, and no area, whether large or small, is to be shut off on which the appliances of science can be brought to bear. Science can not exclude man from the range of investigation; can not on any warrant supplied by the conditions of its own procedure, draw a line within the circumference of nature, even though it may be constrained to allow that there are many things within nature of which it can offer no explanation.

That science has by recent research done much to explain phases of human activity previously unexplained, may be clearly shown. The modification of previously received opinion may be indicated thus,--that many forms formerly regarded as in the true sense voluntary, and so described in the life not only of man, but also of the higher animals, can be explained by the action of brain and nerve. This involves a considerable extension of the area of the mechanical in human action, and a considerable restriction of the area of the voluntary. In seeking to indicate roughly the form of this restriction, we may find enough for our purpose in the distinction between what we may describe as _muscular action_, and what we would more naturally denominate _personal conduct_. This contrast will serve throughout, as we proceed to estimate the explanations which science has reached in dealing with the characteristics of human life.

The proved superiority of brain and nerve in man affords an adequate explanation of his generally recognized superiority in the variety of the forms of his muscular activity. In mere muscular power man can not compete with the more powerful animals. His practical superiority is seen in manipulation and the vastly greater variety of occupations to which he can turn; and in the greater wisdom he has for self-government. Leaving meanwhile out of account comparative intelligence, we have only to consider the superior use man has of the general sensibilities of the body, and of the special senses of touch and sight; the greater variety of the joints and muscles in his body; the more complicated arrangements of his nerve system; and the relation of all these in a single economy, in order to perceive a distinct phase of the superiority of man, sufficiently accounted for by clearly recognized facts, anatomical and physiological. In a multitude of well-known forms of action, of which the mechanical arts afford illustration, man can do what can not be attempted by lower forms of organism.

Another step higher is taken by the advance of physiological science, involving an explanation of _acquired aptitudes_. The interaction of sensibility and motor activity has been shown to be great. A message conveyed along a sensory line is readily transferred to a motor line; the sense of touch becomes a natural guide to familiar forms of action; a form of sensibility may thus be connected with a given range of motor apparatus, just as the history of the blind illustrates how much more can be accomplished by aid of touch without sight, than is ordinarily achieved. By these means, what at first requires consideration and care (neither of which is accounted for by physiological explanations), comes at last to be done without deliberation, and with so much facility, that it does not seem to engage much attention. Physiological science thus accounts for a considerable amount of superior activity characteristic of man in his daily engagements. It must, however, be noticed that the explanation is not a complete one, inasmuch as the action of the sensory and motor apparatus referred to, presupposes consideration and care, that is intellectual and voluntary guidance commensurate with the initial difficulties of attainment, in order that the nerve system may be brought to accomplish what becomes possible afterwards by mere mechanical and chemical contrivance within the living organism.