364 



NATURE 



{Sept. 3, 1874 



complexity be so jirodiiced ? Why, in fact, may it not be that 

 the whole of man's physical actions arc mechanical, his mind 

 living apart, as it were, and only occasionally interfering by 

 means of volition ? " And it so happened that Descartes was 

 led by some of his speculations to believe that beasts had no 

 souls, and consequently could have no consciousness ; and thus, 

 his two ideas harmonising together, he developed that famous 

 hypothesis of the automatism of brutes, which is the main sub- 

 ject of my present discourse. What Descartes meant by this 

 was that animals are absolute machines, as if they were mills or 

 barrel organs ; that they have no feelings ; that a dog does not 

 see, and does not hear, and does not smell, but that the impres- 

 sions which would produce those states of consciousness in our- 

 selves, give rise in the dog, by a mechanical rcllex process, to 

 actions which correspond to those which we perform when we 

 do smell, and do taste, and do see. On the face of it this ap- 

 pears to be a most surprising hypothesis, and I do not wonder 

 that it proved to be a stumbling-block even to such acute and 

 subtle men as Henry More, who was one of Descartes' corre- 

 spondents ; and yet it is a very singular thing that this, the 

 boldest and most paradoxical notion which Descartes broached, 

 has received as much and as strong support from modern physio- 

 logical research as any other of his hypotheses. I will endea- 

 vour to explain to you in as few words as possible what is the 

 nature of that support, and why it is that Descartes' hypothesis, 

 although I am bound to say I do not agree with it, nevertheless, 

 remains at this present time not only quite as defensible as it was 

 in his own time, but I should say, upon the whole, a little more 

 defensible. 



If it should happen to a man that by accident his spinal 

 cord is divided, he would become paralysed below the point 

 of injuiy. In such case his limbs would be absolutely para- 

 lysed ; he would have no control over them, and they would 

 be devoid of sensation. Vou might prick his feet, or burn them, 

 or do anything else you like with them, and they would be abso- 

 lutely insensible. Consciousness, therefore, so far as we can have 

 any knowledge of it, would be entirely abolished in that part of 

 the central nervous apparatus which lies below the injury. But 

 although the man under these circumstances is paralysed in the 

 sense of not being able to move his own limbs, he is not para- 

 lysed in the sense of their being deprived of motion, for if you 

 tickle the soles of his feet with a feather the limbi v/ill be drawn 

 up just as vigorously, perhaps a little more vigorously, than when 

 he was in full possession of the consciousness of what happened 

 to him. Now, that is a retlex action. The impression is 

 transmitted from the skin to the spinal cord, it is reflected from 

 the spinal cord, and passes down into the muscles of the limbs, 

 and they are dragged up in this manner — dragged away from the 

 sources of irritation, though the action, you will observe, is a 

 purely automatic or mechanical action. Suppose we deal with 

 a frog in the same way, and cut across the spinal cord. The 

 frog falls into precisely the same condition. So far as the frog 

 is concerned, his limbs are useless ; but you have merely to apply 

 the slightest irritation to the skin of the foot, and the limb is in- 

 stantly drawn away. Now, if we have any ground for argument 

 at all, we have a right to assume that, under these circum- 

 stances, the lower half of the frog's body is as devoid of con- 

 sciousness as is the lower half of the man's body ; and that the 

 body of the frog below the injury is in this case absolutely de- 

 void of consciousness, is a mere machine like a nmsical box or a 

 barrel-organ, or a watch. You will remark, moreover, that the 

 movement of the limbs is purposive— that is to say, that when 

 you irritate the skin of the foot, the foot is drawn .away from the 

 danger, just as it would be if the frog were conscious and 

 rational, and could act in accordance with rational conscious- 

 ness, Hut you may say it is easy enough to understand how so 

 simple an action might take place mechanically. 



Let us consider another experiment. Take this creature, which 

 ceitainly cannot feel, and touch the skin of the side of the body 

 with a little acetic acid, a little vinegar, which in a frog that could 

 feel would give rise to great pain. In this case there can be no 

 pain, because the application is made below the point of section; 

 nevertheless, the frog lifts up the limb of the same side, and ap- 

 plies the foot to rubbing off the acetic acid ; and, what is still 

 more remarkable, if you hold down the limb so that the frog 

 cannot use it, he will, by and by, take the limb of the other side 

 and turn it across the body, and use it for the same rubliing pro- 

 cess. It is impossible that the frog, if it were in its entirety and 

 were reasoning, could 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 con- 



sciousness, is a mere automatic machine. But now suppose 

 that instead of making your section of the cord in the middle 

 of the body, you had made it in such a manner as to divide the 

 hindermost part of the brain from the foremost part of the brain, 

 and suppose the foremost two-thirds of the brain entirely taken 

 away, the frog is then absolutely devoid of any spontaneity ; it 

 will remain for ever where you leave it ; it will not stir unless it 

 is touched ; it sits upright in the condition in which a frog habi- 

 tually does sit ; but it differs from the frog which I have just 

 described in this, that if you throw it into the water it begins to 

 swim — swims just as well as the perfect frog does. Now, 

 swimming, you know, requires the combination, and indeed the 

 very careful and delicate combination, of a great number of 

 muscular actions, and the only way we can account for this is, 

 that the impression made upon the sensory nerves of the skin of 

 the frog by the contact of the water, conveys to the central 

 nervous apparatus a stimulus which sets going a certain machinery 

 by which all the muscles of swimming are brought into play in 

 due order and succession. Moreover, if the frog be stimulated, 

 be touched by some irritating body, although we are quite certain 

 it cannot feel, it jumps or walks as well as the complete frog can 

 do. But it cannot do more than this. 



Suppose yet one other experiment. Suppose that all that is taken 

 away of the brain is what we call the cerebral hemispheres, the 

 most anterior part of the brain. If that operation is properly per- 

 formed, the frog may be kept in a state of full bodily vigour for 

 montlis, or it may be for years ; but it will sit for ever in the same 

 spot. It sees nothing; it hears nothing. It will starve sooner than 

 feed itself, although if food is put into its mouth it swallows it. 

 On irritation it jumps or walks ; if thrown into the water it swims. 

 But the most remarkable thing that it does is this — you put it in 

 the flat of your hand ; it sits there, crouched, perfectly quiet, and 

 would sit there for ever. Then if you incline your hand, doing 

 it very gently and slowly, so that the frog would naturally tend 

 to slip off, you feel the creature's fore-paws getting a little slowly 

 on to the edge of your hand until he can just hold himself there, 

 so th.it he does not fall ; then, if you turn your hand, he mounts 

 up with great care and deliberation, putting one leg in front and 

 then another, until he balances himself with perfect precision 

 upon the edge of your hand ; then if you turn your hand over, he 

 goes through the opposite set of operations until he comes to sit 

 in perfect security upon the back of your hand. The doing of 

 all this requires a delicacy of co-ordination, and an adjustment 

 of the muscular apparatus of the body which is only comparable 

 to that of a rope-dancer among ourselves ; though in truth a frog 

 is an animal very poorly constiiicted for rope-dancing, and on 

 the whole we may give him rather more credit than we should 

 to a human dancer. These movements are performed with the 

 utmost steadiness and precision, and you may vary the position 

 of your hand, and the frog, so long as you arc reasonably slow 

 in your movements, will work backwards and forwards like a 

 clock. And what is still more wonderful is, that if you put the 

 frog on a table, and put a book between him and the light, and 

 give him a little jog behind, he will jump — take a long jump, 

 very possibly — but he won't jump against the book ; he will 

 jump to the right or to tlie left, but he will get out of the way, 

 showing that although he is absolutely insensible to ordinary im- 

 pressions of light, there is still a something which passes through 

 the sensory nerve, acts upon the machinery of his nervous system, 

 and causes it to adapt itself to the proper action. 



Can we go further than this? I need not say that since those days 

 of commencing anatomical science when criminals were handed 

 over to the doctors, we cannot make experiments on human beings, 

 but sometimes they are made for us, and made in a very remarkable 

 manner. That operation called war is a great series of physio- 

 logical experiments, and sometimes it happens that these physio- 

 logical experiments bear very remarkable fruit. I am indebted 

 to my friend General Strachey for bringing to my notice an 

 account of a case which appeared within the last four or five days 

 in the scientific article of the Joiiriial ,/,s DLbats. A French 

 soldier, a sergeant, was wounded at tlie battle of Bazeilles, one, 

 as you recollect, of the most fiercely contested battles of the late 

 war. The man was shot in the head, in the region of what we 

 call the left parietal bone. The bullet fractureil the bone. The 

 sergeant had enough vigour left to send his bayonet through the 

 Prussian who shot him. Then lie wandered a few hundred yards 

 out of the village, fell senseless, but, after the action, was picked up 

 and taken to the hospital, where he remained some time. When 

 he came to himself, as usual in such cases of injury, he was para- 

 lysed on the opposite side of the body, that is to say, the right 

 arm and the right leg were completely paralysed. That state of 



