642 THE BRAIN. 



if a morsel be placed within its mouth it at once begins to eat. When stirred 

 it will with ease and steadiness run or leap forward ; and obstacles in its 

 course are very frequently, with more or less success, avoided. In some cases 

 the animal (rat) has been described as following by movements of the head a 

 bright light held in front of it (provided that the optic nerves and tracts 

 have not been injured during the operation), as starting when a shrill and 

 loud noise is made near it, and as crying when pinched, often with a long 

 and seemingly plaintive scream. So plaintive is the cry which it thus gives 

 forth as to suggest to the observer the existence of passion ; this, however, is 

 probably a wrong interpretation of a vocal action ; the cry appears plaintive 

 simply because, in consequence of the completeness of the reflex nervous 

 machinery and the absence of the usual restraints, it is prolonged. 



Without insisting too much on such results as these, and allowing full 

 weight to the objection which may be urged, that in some of these cases 

 parts of the cerebral hemispheres surrounding the optic thalami were left, 

 there still remains adequate evidence to show that a mammal such as a 

 rabbit, in the same way as a frog and a bird, may in the complete or all but 

 complete absence of the cerebral hemispheres maintain a natural posture, 

 free from all signs of disturbance of equilibrium, and is able to carry out 

 with success, at all events all the usual and common bodily movements. 

 And as in the bird and frog, the evidence also shows that these movements 

 not only may be started by, but in their carrying out are guided by and 

 coordinated by afferent impulses along afferent nerves, including those of the 

 special senses. But in the case of the rabbit it is even still clearer than in 

 the case of the bird that the effects of these afferent impulses are different 

 from those which result when the impulses gain access to an intact brain. 

 The movements of the animal seem guided by impressions made on its retina, 

 as well as on other sensory nerves ; we may perhaps speak of the animal as 

 the subject of sensations ; but there is no satisfactory evidence that it pos- 

 sesses either visual or other perceptions, or that the sensations which it ex- 

 periences give rise to ideas. Its avoidance of objects depends not so much 

 on the form of these as on their interference with light. No image, whether 

 pleasant or terrible, whether of food or of an enemy, produces an effect on 

 it, other than that of an object reflecting more or less light. And we may 

 infer that it lacks the possession of an intelligent will. But it must always 

 be remembered that some of the phenomena are due to the operation pro- 

 ducing other results than the mere absence of the part removed. We roust 

 bear in mind that in all the above experiments, while the positive phenomena, 

 the things which the animal continues able to do, are of great value, the 

 negative phenomena, the things which the animal can no longer do, are of 

 much less, indeed of doubtful value. The more carefully and successfully 

 the experiments are carried out, the narrower become what we may call the 

 " deficiency phenomena," the phenomena which are alone and directly due 

 to something having been taken away. Were it possible to keep the rabbit 

 alive long enough for the mere effects of the operation to pass completely 

 away, we should not only probably witness, as in the case of the bird, a 

 greater scope of movement and more frequent spontaneity, but possibly find 

 a difficulty in describing the exact condition of the animal. 



554. Hitherto attempts to witness similar phenomena in more highly 

 organized- mammals, such as the dog, have failed ; these animals do not 

 recover from the operation of removing the whole of both their hemispheres 

 sufficiently to enable us to judge whether they, like the frog, the bird, and 

 the rabbit, can carry out coordinate bodily movements in the absence of the 

 hemispheres, or whether in them this part of the brain, so largely developed, 

 has usurped functions which in the lower animals belong to other parts. 



