"Les extrêmes se touchent; "the shibboleth of materialists that "thought is a secretion of the brain," is the Fichtean doctrine that "the phenomenal universe is the creation of the Ego," expressed in other language. IV. The motion of the matter of a sensory nerve may be transmitted through the brain to motor nerves, and thereby give rise to contraction of the muscles to which these motor nerves are distributed; and this reflection of motion from a sensory into a motor nerve may take place without volition, or even contrary to it. And that nevertheless it will be hard to keep from winking. And this shows, that it is not by the agency of the soul that the eyes shut, since this action is contrary to that volition which is the only, or at least the chief, function of the soul; but it is because the mechanism of our body is so disposed, that the motion of the ment in our brain, and this sends the animal hand towards our eyes excites another movespirits into those muscles which cause the eyelids to close. Since Descartes' time, experiment has eminently enlarged our knowledge of the details of reflex action. The discovery of Bell has enabled us to follow the tracks of the sensory and motor impulses, along distinct bundles of nerve-fibres; and the been proved to be a great centre of reflex remains as Descartes left it, and it is one action; but the fundamental conception of the pillars of nerve-physiology at the present day. V. In stating these important truths, Des-spinal cord, apart from the brain, has cartes defined that which we now term "reflex action." Indeed he almost uses the term itself, as he talks of the "animal spirits 66 as réfléchis," " from the sensory into the motor nerves. this use of the word "reflected" was no mere accident, but that the importance and appropriateness of the idea it suggests was fully understood by Descartes' contemporaries, is apparent from a passage in Willis' well-known essay, "" De Anima Brutorum," published in 1672, in which, in giving an account of Descartes' views, he speaks of the animal spirits being diverted into motor channels, “velut undulatione reflexâ.” † Nothing can be clearer in statement, or in illustration, than the view of reflex action which Descartes gives in the "Passions de l'Ame," Art. xiii. After recapitulating the manner in which sensory impressions transmitted by the sensory nerves to the brain give rise to sensation, he proceeds: And in addition to the different feelings excited in the soul by these different motions of the brain, the animal spirits, without the intervention of the soul, may take their course towards certain muscles, rather than towards others, and thus move the limbs, as I shall prove by an example. If some one moves his hand rapidly towards our eyes, as if he were going to strike us, although we know that he is a friend, that he does it only in jest, and that he will be very careful to do us no harm, The motion of any given portion of the matter of the brain excited by the motion of a sensory nerve, leaves behind a readiness to be moved in the same way, in that part. Anything which resuscitates the motion gives rise to the appropriate feeling. This is the physical mechanism of memory. Descartes imagined that the pineal side of the brain, the function of which, body (a curious appendage to the upper if it have any, is wholly unknown) was the instrument through which the soul nicated them to, the brain. And he thus received impressions from, and commuendeavours to explain what happens when one tries to recollect something: : Thus when the soul wills to remember any. thing, this volition, causing the [pineal] gland to incline itself in different directions, drives the [animal] spirits towards different regions of the brain, until they reach that part in which are the traces, which the object which it desires to remember has left. These traces are produced thus: those pores of the brain through which the [animal] spirits have previously been driven, by reason of the presence of the object, have thereby acquired a tendency to be opened by the animal spirits which return towards them, more easily than other pores, so that the animal spirits, impinging on these pores, enter them more readily than others. By this means they excite a particular movement in the pineal gland, which represents the object to the soul, and causes it to know what it is which it de sired to recollect.* * Les Passions de l' Ame, xlii.} That memory is dependent upon some which are stated by Descartes have simcondition of the brain is a fact estab-ply been more clearly defined, more fully lished by many considerations-among illustrated, and, for the most part, demonthe most important of which are the re-strated, by modern physiological research. markable phenomena of aphasia. And But there remains a doctrine to which that the condition of the brain on which Descartes attached great weight, so that memory depends, is largely determined full acceptance of it became a sort of by the repeated occurrence of that condi- note of a thorough-going Cartesian, but tion of its molecules, which gives rise to which, nevertheless, is so opposed to orthe idea of the thing remembered, is no dinary prepossessions that it attained less certain. Every boy who learns his more general notoriety, and gave rise to lesson by repeating it exemplifies the more discussion, than almost any other fact. Descartes, as we have seen, sup- Cartesian hypothesis. It is that doctrine, poses that the pores of a given part of that brute animals are mere machines or the brain are stretched by the animal automata, devoid not only of reason, but spirits, on the occurrence of a sensation, of any kind of consciousness, which is and that the part of the brain thus stated briefly in the " Discours de la Méstretched, being imperfectly elastic, does thode," and more fully in the "Réponses not return to exactly its previous condi- aux Quatrièmes Objections," and in the tion, but remains more distensible than correspondence with Henry More.* it was before. Hartley supposes that the The process of reasoning by which vibrations, excited by a sensory, or other, Descartes arrived at this startling concluimpression, do not die away, but are rep-sion is well shown in the following pasresented by smaller vibrations or "vibra-sage of the "Réponses:". tiuncules," the permanency and intensity So of which are in relation with the fre- this is not the place for considering them, But as regards the souls of beasts, although quency of repetition of the primary vibra- and though, without a general exposition of tions. Haller has substantially the same physics, I can say no more on this subject idea, but contents himself with the gen-than I have already said in the fifth part of eral term 66 mutationes," to express the my treatise on method; yet, I will further cerebral change which is the cause of a state, here, that it appears to me to be a very state of consciousness. These "muta- remarkable circumstance that no movement tiones" persist for a long time after the can take place, either in the bodies of beasts, cause which gives rise to them has ceased or even in our own, if these bodies have not in themselves all the organs and instruments to operate, and are arranged in the brain according to the order of coexistence and would be accomplished in a machine. by means of which the very same movements succession of their causes. And he gives that, even in us, the spirit, or the soul, does these persistent "mutationes" the pictu- not directly move the limbs, but only deterresque name of “vestigia rerum,” quemines the course of that very subtle liquid non in mente sed in ipso corpore et in me-which is called the animal spirits, which, rundulla quidem cerebri ineffabili modo in-ning continually from the heart by the brain credibiliter minutis notis et copia infinita, into the muscles, is the cause of all the moveinscriptæ sunt." I do not know that ments of our limbs, and often may cause many any modern theory of the physical condi-different motions, one as easily as the other. And it does not even always exert this detions of memory differs essentially from termination; for these, which are all children-mutatis take place in us, there are many which do not the movements which among mutandis of the Cartesian doctrine. depend on the mind at all, such as the beating Physiology is, at present, incompetent to of the heart, the digestion of food, the nutrisay anything positively about the matter, tion, the respiration, of those who sleep; and, or to go further than the expression of even in those who are awake, walking, singthe high probability, that every molecular ing, and other similar actions, when they are change which gives rise to a state of con-performed without the mind thinking about sciousness, leaves a more or less persist-them. And, when one who falls from a height ent structural modification, through which the same molecular change may be regenerated by other agencies than the cause which first produced it. Thus far, the propositions respecting the physiology of the nervous system Haller, Prima Linea, ed. iii. Sensus Interni dlviii. throws his hands forwards to save his head, it is in virtue of no ratiocination that he performs this action; it does not depend upon his mind, but takes place merely because his senses being affected by the present danger, some change arises in his brain which de Réponse de M. Descartes à M. Morus. 1649. Euvres, tome x. p. 204. "Mais le plus grand de tous les préjugés que nous ayons retenus de notre enfance, est celui de croire que les bêtes pensent," &c. termines the animal spirits to pass thence into the nerves, in such a manner as is required to produce this motion, in the same way as in a machine, and without the mind being able to hinder it. Now since we observe this in our selves, why should we be so much astonished if the light reflected from the body of a wolf into the eye of a sheep has the same force to excite in it the motion of flight? The Port-Royalists adopted the hypothesis that brutes are machines, and are said to have carried its practical applications so far as to treat domestic animals with neglect, if not with actual cruelty. As late as the middle of the eighteenth century, the problem was discussed very fully and ably by Bouillier, in his "Essai philosophique sur l'Ame des Bêtes," while Condillac deals with it in his "Traité des Animaux;" but since then it has received little attention. Nevertheless, After having observed this, if we wish to learn by reasoning, whether certain movements of beasts are comparable to those which are effected in us by the operation of the mind, or, on the contrary, to those which de-modern research has brought to light a pend only on the animal spirits and the dis- great multitude of facts, which not only position of the organs, it is necessary to show that Descartes' view is defensible, consider the difference between the two, which I have explained in the fifth part of the dis- but render it far more defensible than it course on method (for I do not think that any was in his day. It must be premised, that it is wholly others are discoverable), and then it will easily be seen, that all the actions of beasts impossible absolutely to prove the presare similar only to those which we perform ence or absence of consciousness in anywithout the help of our minds. For which thing but one's own brain, though, by reason we shall be forced to conclude, that we analogy, we are justified in assuming its know of the existence in them of no other existence in other men. Now, if by some principle of motion than the disposition of accident, a man's spinal cord is divided, their organs and the continual affluence of his limbs are paralyzed, so far as his animal spirits produced by the heat of the volition is concerned, below the point of heart, which attenuates and subtilizes the blood; and, at the same time, we shall ac-injury; and he is incapable of experienknowledge that we have had no reason forcing all those states of consciousness, assuming any other principle, except that, not which, in his uninjured state, would be exhaving distinguished these two principles of cited by irritation of those nerves which motion, and seeing that the one, which de- come off below the injury. If the spinal pends only on the animal spirits and the cord is divided in the middle of the back, organs, exists in beasts as well as in us, we for example, the skin of the feet may be have hastily concluded that the other, which depends on mind and on thought, was also cut, or pinched, or burned, or wetted with vitriol, without any sensation of touch, possessed by them. or of pain, arising in consciousness. So Descartes' line of argument is per-far as the man is concerned, therefore, the fectly clear. He starts from reflex action part of the central nervous system which in nian, from the unquestionable fact lies beyond the injury is cut off from conthat, in ourselves, co-ordinate, purposive, sciousness. It must indeed be admitted, actions may take place, without the inter- that, if any one think fit to maintain that vention of consciousness or volition, or the spinal cord below the injury is coneven contrary to the latter. As actions scious, but that it is cut off from any of a certain degree of complexity are means of making its consciousness known brought about by mere mechanism, why to the other consciousness in the brain, may not actions of still greater complex- there is no means of driving him from ity be the result of a more refined mech- his position by logic. But assuredly anism? What proof is there that brutes there is no way of proving it, and in the are other than a superior race of mari- matter of consciousness, if in anything, onettes, which eat without pleasure, cry we may hold by the rule, "De non appawithout pain, desire nothing, know noth-rentibus et de non existentibus eadem est ing, and only simulate intelligence as a ratio." However near the brain the spibee simulates a mathematician? * • Malebranche states the view taken by orthodox Cartesians in 1689 very forcibly: "Ainsi dans les chiens, les chats, et les autres animaux, il n'y a ny intelligence, ny âme spirituelle comme on l'entend ordinairement. Ils mangent sans plaisir; ils crient sans douleur ; ils croissent sans le sçavoir; ils ne désirent rien; ils ne connoissent rien; et s'ils agissent avec adresse et d'une manière qui marque l'intelligence, c'est que Dieu les faisant pour les conserver, il a conformé leurs corps de telle manière, qu'ils évitent organiquement, sans le sçavoir, tout ce qui peut les détruire et nal cord is injured, consciousness re- able conclusion, that consciousness in man depends upon the integrity of the anterior division of the brain, while the middle and hinder divisions of the brain, and the rest of the nervous centres, have nothing to do with it. And it is further highly probable, that what is true for man is true for other vertebrated animals. man, on which experiments can be made without remorse; as we have a right to conclude that a frog's spinal cord is not likely to be conscious, when a man's is not. Now the frog behaves just as the man did. The legs are utterly paralyzed, so far as voluntary movement is concerned; but they are vigorously drawn up to the body, when any irritant is applied to the foot. But let us study our frog a little further. Touch the skin of the side of the body with a little acetic acid, which gives rise to all the signs of great pain in an uninjured frog. In this case there can be no pain, because the application is made to a part of the skin supplied with nerves which come off from the cord below the point of section; nevertheless, the frog lifts up the limb of the same side, and applies the foot to rub off the acetic acid; and, what is still more remarkable, if the limb be held so that the frog cannot use it, it will, by-and-by, move the limb of the other side, turn it across the body, and use it for the same rubbing process. It is impossible that the frog, if it were in its entirety and could reason, should perform actions more purposive than these; and yet we have most complete assurance that, in this case, the frog is not acting from purpose, has no consciousness, and is a mere automatic machine. We may assume, then, that in a living vertebrated animal, any segment of the cerebro-spinal axis (or spinal cord and brain) separated from that anterior division of the brain which is the organ of consciousness, is as completely incapable of giving rise to consciousness, as we know it to be incapable of carrying out volitions. Nevertheless, this separated segment of the spinal cord is not passive and inert. On the contrary, it is the seat of extremely remarkable powers. In our imaginary case of injury, the man would, as we have seen, be devoid of sensation in his legs, and would have not the least power of moving them. But, if the soles of his feet were tickled, the legs would be drawn up, just as vigorously as they would have been before the injury. We know exactly what happens when the soles of the feet are tickled; a molecular change takes place in the sensory nerves of the skin, and is propagated along them and through the posterior roots of the spinal nerves, which are constituted by them, to the grey matter of the spinal cord. By means of that grey matter the But now suppose that, instead of makmolecular motion is reflected into the ing a section of the cord in the middle anterior roots of the same nerves, consti- of the body, it had been made in such a tuted by the filaments which supply the manner as to separate the hindermost muscles of the legs, and, travelling along division of the brain from the rest of the these motor filaments, reaches the mus-organ, and suppose the foremost twocles, which at once contract, and cause the limbs to be drawn up. thirds of the brain entirely taken away. The frog is then absolutely devoid of any spontaneity; it sits upright in the attitude which a frog habitually assumes; and it will not stir unless it is touched; but it differs from the frog which I have just described in this, that, if it be thrown into the water, it begins to swim, and In order to move the legs in this way, a definite co-ordination of muscular contractions is necessary; the muscles must contract in a certain order and with duly proportioned force; and moreover, as the feet are drawn away from the source of irritation, it may be said that the ac-swims just as well as the perfect frog tion has a final cause, or is purposive. Thus it follows, that the grey matter of the segment of the man's spinal cord, though it is devoid of consciousness, nevertheless responds to a simple stimulus by giving rise to a complex set of muscular contractions, co-ordinated towards a definite end, and serving an obvious purpose. does.. But swimming requires the combination and successive co-ordination of a great number of muscular actions. And we are forced to conclude, that the impression made upon the sensory nerves of the skin of the frog by the contact with the water into which it is thrown, causes the transmission to the central nervous apparatus of an impulse, which If the spinal cord of a frog is cut sets going a certain machinery by which across, so as to provide us with a seg-all the muscles of swimming are brought ment separated from the brain, we shall into play in due co-ordination. If the have a subject parallel to the injured frog be stimulated by some irritating body, it jumps or walks as well as the complete frog can do. The simple sensory impression, acting through the machinery of the cord, gives rise to these complex combined movements. The habits of a frog, leading its natural life, involve such simple adaptations to surrounding conditions, that the machinery which is competent to do so much, automatically, might well do all. And this argument is vastly strengthened by what has been learned in recent times of the marvellously complex operations which are performed mechanically, and to all appearance without consciousness, by men, when, in consequence of injury or disease, they are reduced to a condition more or less comparable to that of a brain has been removed. A case has recently been published by an eminent French physician, Dr. Mesnet, which illustrates this condition so remarkably, that I make no apology for dwelling upon it at considerable length.* It is possible to go a step further. Suppose that only the anterior division of the brain -so much of it as lies in front of the "optic lobes "- is removed. If that operation is performed quickly and skilfully, the frog may be kept in a state of full bodily vigour for months, or it may be for years; but it will sit unmoved. It sees nothing; it hears noth-frog, in which the anterior part of the ing. It will starve sooner than feed itself, although food put into its mouth is swallowed. On irritation, it jumps or walks; if thrown into the water it swims. If it be put on the hand, it sits there, crouched, perfectly quiet, and would sit there forever. If the hand be inclined A sergeant of the French army, Fvery gently and slowly, so that the frog twenty-seven years of age, was wounded would naturally tend to slip off, the crea- during the battle of Bazeilles, by a ball ture's fore paws are shifted on to the which fractured his left parietal bone. edge of the hand, until he can just pre- He ran his bayonet through the Prussian vent himself from falling. If the turning soldier who wounded him, but almost of the hand be slowly continued, he immediately his right arm became paramounts up with great care and delibera-lyzed; after walking about two hundred tion, putting first one leg forward and then another, until he balances himself with perfect precision upon the edge; and, if the turning of the hand is continued, over he goes through the opposite set of operations, until he comes to be seated in security, upon the back of the hand. The doing of all this requires a delicacy of co-ordination, and precision of adjustment of the muscular apparatus of the body, which is only comparable to that of a rope-dancer. To the ordinary influences of light, the frog, deprived of its central hemispheres, appears to be blind. Nevertheless, if the creature be put upon a table with a book at some little distance between it and the light, and the skin of the hinder part of its body is then irritated, it will jump forward, avoiding the book by passing to the right or left of it. Although the frog, therefore, appears to have no sensation of light, visible objects act through its brain upon the motor mechanism of its body.* It is obvious, that had Descartes been acquainted with these remarkable results of modern research, they would have furnished him with far more powerful arguments than he possessed in favour of bis view of the automatism of brutes. See the remarkable essay of Göltz, Beiträge zur Lehre von den Functionen der Nervencentren des Frosches, published in 1869. I have repeated Göltz's experiments, and obtained the same results. yards, his right leg became similarly affected, and he lost his senses. When he recovered them, three weeks afterwards, in hospital at Mayence, the right half of the body was completely paralyzed, and remained in this condition for a year. At present, the only trace of the paralysis which remains is a slight weakness of the right half of the body. Three or four months after the wound was inflicted, periodical disturbances of the functions of the brain made their appearance, and have continued ever since. The disturb ances last from fifteen to thirty hours; the intervals at which they occur being from fifteen to thirty days. For four years, therefore, the life of this man has been divided into alternating phases- short abnormal states intervening between long normal states. In the periods of normal life, the exsergeant's health is perfect; he is intelligent and kindly, and performs, satisfactorily, the duties of a hospital attendant. The commencement of the abnormal state is ushered in by uneasiness and a sense of weight about the forehead which the De l'Automatisme de la Mémoire et du Souvenir, dans le Somnambulisme pathologique. Par le Dr. E. Mesnet, Médecin de l'Hopital Saint-Antoine. L'Union Médicale, Juillet 21 et 23, 1874. My attention was first called to a summary of this remarkable case, which appeared in the Journal des Débats for the 7th of August, 1874, by my friend General Strachey. F.R.S. |