The Relations of Science and Religion Part 7

Regarded as the great central organ, the brain is divided into two halves or hemispheres, from each one of which goes forth supply of nerve fibres and nerve energy for the opposite side of the body. Its greatest depth is in the central part, the front and back being rounded down, the frontal region being, however, considerably more ma.s.sive than the rear.

Besides this great central body, there are several dependent subordinate bodies, placed underneath, and directly above the upper part of the spine. Most important of these is the _cerebellum_, or little brain, whose functions are now generally believed to be closely connected with the equilibrium of the body when moving. Somewhat nearer the centre, and quite under the brain proper is the _pons_ or bridge, providing for the interlacing of the fibres on their way out from the the central organ, and just below that are certain elongated bodies (_medulla oblongata_), consisting of ma.s.ses of fibre just above the spinal cord.

Before closing this very brief and hasty description of the nerve system, there is one peculiarly striking arrangement to which special reference may be made. The ma.s.s of nerve fibre which pa.s.ses down within the back-bone const.i.tuting the spinal column, which is formed in two divisions equivalent to the hemispheres of the brain, gives out at each of the vertebrae or spinal joints a supply of nerve for the portion of the body contiguous. This supply is sent out from each side of the column, and issues in two roots, a posterior and anterior; the posterior root being a body of sensory nerves, the anterior root of motor nerves.

Shortly after pa.s.sing out, these two form into one, uniting to const.i.tute a nerve trunk. Just after they have thus united, the trunk again opens up into two, and in each one of these two a share of the sensory and motor roots finds a place, and thus preparation is made for sending out towards both the front and back of the body suitable proportion of both sets of nerves. The two roots drawn together as if to bind them into one, are by some inexplicable process subdivided, and the two bands issuing from the united band are found to have each a share of the contents of each root. Of all the singular occurrences coming under scientific observation there is nothing more surprising. The fact is certain, but there is no scientific explanation of the contrivance by which such a singular result is secured.

[Ill.u.s.tration: BRAIN OF THE CRAB.]

[Ill.u.s.tration: BRAIN OF THE COD, THE TWO LARGER LOBES BEING THOSE OF VISION, THE BRAIN BEING IN FRONT OF THESE.]

Having now before us in outline a representation of the nervous system of man, and having in this a guide to the understanding of the prominent features involved in the distribution of two orders of nerves over the body, and their concentration in a central organ, we are prepared for considering the comparative brain development presented to view as we ascend the scale of animal life. The main features of gradation may be shortly stated. In all cases, the brain is a soft pulpy body, composed as described, the exterior portion being cellular tissue, the interior fibrous, from the gathering of nerve lines. In the lowest orders of animals, the brain is of very small size. In the _insects_, such as the ant, bee, and wasp, it is only a slight band stretching from eye to eye.

In the whole order of _fishes_ an advance in organization appears, though the brain is small relatively to the size of the body, a fact which seems readily explained by the fact that there is little articulation in the structure of the fish, the whole body moving in one ma.s.s, by simple management of the fins and tail. The brain as a rule is simply two small round lobes of smooth surface laid together; and what is most to be remarked is that the brain proper is quite inferior in size to lobes of vision.[CT] In front of the brain are slight strands connected with the organ of smell; and behind it are the two large lobes known as optic lobes, before which the brain appears comparatively insignificant. This is the ordinary arrangement, but in the case of the shark the brain extends to much larger proportions, greatly surpa.s.sing the optic lobes, and having in front of it unusually ample provision for the organ of smell.[CU]

When we reach the _reptiles_ the normal order appears which continues thereafter up the whole range of animal life. The brain takes precedence of the lobes of special sense, and is the most important organ. This appears quite decisively in the brain of the frog. On account of the possession of four limbs, and its power of locomotion by forward leaps, provided for by the superior size and strength of the hind legs, there is much greater need for distribution of nerve lines, to place distinct muscles under control, and as a consequence the brain or central organ a.s.sumes a position of greater importance.

[Ill.u.s.tration: BRAIN OF THE BIRD.]

[Ill.u.s.tration: BRAIN OF THE CAT, WITH BULB OF SMELL IN FRONT, AND LITTLE BRAIN BEHIND.]

Pa.s.sing next to _birds_, we find a marked advance in the structure of the brain. The two hemispheres are considerably extended towards the rear, and the two optic lobes underneath the back part of the brain are separated from each other, being placed somewhat to the side. The cerebellum, or little brain, regulating equilibrium becomes more important in size and form, being laid up in transverse furrows. These important advances indicate a life of much more varied activity than in the lower orders. This animal walks, hops, perches on branches by the clutching of its claws, and flies from place to place. To provide for these varied forms of activity, there must be a more detailed arrangement of nerve system, which is clearly indicated in the complexity of the central organ.

The next advance introduces to notice the _smaller quadrupeds_, known as the rodents, of which the rat, rabbit, and hare may be taken as the most familiar examples. Here we still have the smooth surface of the brain, without any subdivision and twining into folds such as afterwards appears, but it is somewhat elongated in shape. An additional element here comes into view, that is, extra provision for acuteness of smell, in accordance with the well-known characteristics of the cla.s.s of animals. Set out in front of the brain are two distinct lobes, which are the olfactory lobes. Wherever these are so placed in front of the brain, it is a clear proof that the life of the animal is largely directed by smell, that is, in a relatively greater degree than by sight, though constantly using the organs of vision with rapidity and acuteness. The cerebellum is in all cases prominent to the rear, presenting the laminated appearance always distinctive of the organ.

We now make a very marked transition in the development of brain, 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 s.p.a.ce 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.

[Ill.u.s.tration: BRAIN OF HORSE, WITH BULB OF SMELL IN FRONT, LITTLE BRAIN IN REAR.]

[Ill.u.s.tration: 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 pa.s.s 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, a.s.sume 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 a.n.a.logous 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 pa.s.s 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]

[Ill.u.s.tration: HUMAN BRAIN]

[Ill.u.s.tration: 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 mult.i.tude 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 ma.s.s 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 mult.i.tude 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 ma.s.sed 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 ma.s.ses 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 coordination 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 ma.s.s, 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 ma.s.ses of nerve, const.i.tuting 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 pa.s.s across to the opposite sides of the body. This gathering is known as the _medulla oblongata._ Just beneath comes the spinal ca.n.a.l, 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 a.n.a.logous 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 a.s.sumption 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 part.i.tion 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 ill.u.s.trative aid, however, consists in nothing more than the suggestion of distinct areas, for there is no a.n.a.logy between what has been discovered by the observations now to be described, and the "b.u.mps" 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 Ma.s.son,--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 s.h.i.+ft 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 cl.u.s.ter 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 cla.s.s 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 pa.s.ses 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 coordinate 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. Pus.h.i.+ng 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 acc.u.mulation 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 h.o.m.ologies of structure there are, and how many a.n.a.logies 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 wors.h.i.+p of "the King eternal, immortal, invisible, the only wise G.o.d"?

FOOTNOTES:

[CS] Protoplasm, see Appendix VII.

[CT] Unless references are otherwise given, ill.u.s.tration 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 acc.u.mulated 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 a.s.signed 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 pus.h.i.+ng 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 antic.i.p.ated 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 pa.s.sed 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 pa.s.sed 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 a.s.sertions. 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 circ.u.mference 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 mult.i.tude of well-known forms of action, of which the mechanical arts afford ill.u.s.tration, 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 apt.i.tudes_. 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 ill.u.s.trates 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.

Having thus briefly indicated the advances in knowledge of the working of our own organism gained by recent research, and the explanation thus afforded of much of the superiority manifest in human life, we come upon the grand difficulty of science,--How to account for _intellectual superiority_. It is obvious that animals give proofs of intelligence as well as men; and that the human brain has a marked superiority in the frontal region, to which intelligence is commonly referred, as it certainly is superior also in the back part of the organ, to which intelligence is not so commonly referred. But the pressing difficulty is this, to show how nerve cells, confessedly concerned with the development of nerve energy, and the production of sensory and motor activity, can be further considered capable of performing the function of thought, covering the whole variety of mental occupations. Attention has been directed to the recognized diversities of nerve cells, which are unipolar, bipolar, and multipolar, on the hypothesis that these diversities may point to differences of function so great as to provide what is required. But there is a total failure of evidence to substantiate this hypothesis. The differences among the nerve cells of the brain are differences in size, and in the number of the lines of communication taking rise from them. In accordance with the plan of arrangement everywhere recognized, the number of protoplasmic lines originating from a cell gives an index to the points of contact it has in the surrounding tissue, and thus to the part it may perform in the work of coordination or interaction. A small cell with only a single line or fibre proceeding from it, must be regarded as a cell conveying nerve stimulus in only a single direction, and to only a single destination. A bipolar cell in accordance with the same rule of interpretation, is a cell having communication in two opposite directions, and thus may be capable of transmitting stimulus by the one channel or by the other, besides which it is possible, so far as structure is concerned, that such a cell may receive stimulus from one direction and send it forth in an opposite, thus proving a centre of intercommunication. On the same plan, a multipolar cell, being of greater size, and having from five to ten fibres proceeding from it, holds a more important place in the manifold ramifications of cellular tissue, sending out stimulus in an increased variety of courses according to the number of the lines pertaining to it, and proving thus an intermediate station in communication with a variety of distinct centres. No observation yet directed upon the nerve cells has proved sufficient to establish all this, but the supposition is in strict harmony with what has been ascertained as to the laws governing the action of the nerve system.