612 - THE BRAINLESS MAMMAL. [BOOK in. 



tracts have not been injured during the operation), and starts 

 when a shrill and loud noise is made near it. When pinched it 

 cries, often with a long and seemingly plaintive scream. Evidently 

 its movements are guided and may be originated by tactile, visual, 

 and auditory sensations 1 . But there is no satisfactory evidence 

 that it possesses either visual or other perceptions, or that the 

 sensations it experiences give rise to ideas. Its avoidance of 

 objects depends not so much on the form of these as on their inter- 

 ference 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 though 

 the plaintive character of the cry which it gives forth when 

 pinched suggests to the observer the existence of passion, it is pro- 

 bable that this is a wrong interpretation of a vocal action ; the cry 

 appears plaintive simply because, in consequence of the complete- 

 ness of the reflex nervous machinery and the absence of the usual 

 restraints, it is prolonged. The animal is able to execute all its 

 ordinary bodily movements, but in its performances nothing is ever 

 seen to indicate the retention of an educated intelligence. With 

 the removal of that part of the brain which lies between the 

 hemispheres and the medulla a large number of these coordinate 

 movements disappear. The animal can no longer balance itself, it 

 lies helpless on its side, and though various movements of a 

 complex character, including cries, may be produced by appropriate 

 stimuli, they are much more limited than when these cerebral 

 structures are intact. 



When in a dog, the cerebral convolutions are removed piece- 

 meal at several operations, the animal may be kept alive and in 

 good health for a long time, many months at least, though these 

 parts of the brain have been reduced to very small dimensions. 

 In such a case the indications of volition are much more prominent 

 and numerous. We do not wish now to discuss whether the residues 

 of volition and of intelligence then observed are to be ascribed to 

 the small portion of the cerebral hemispheres still left, or whether 

 they result from the working of other parts of the brain. To do this 

 we should have to attempt to define with greater exactness than we 



1 Here we come upon a difficulty, which we shall meet with again in the present 

 chapter. Are we justified in speaking of 'sensation' in cases where we have reason 

 to think that consciousness is absent, or where, as in the present instance, we have 

 no evidence to shew whether consciousness is present or not ? In treating of the 

 senses we called attention to the fact, that we must suppose in the case, for instance, 

 of vision, the visual peripheral organ to be connected with a visual central organ in 

 such a way that the sensory impulses originating in the former become modified in 

 the latter before they affect consciousness. In the peripheral organ and along the 

 nerve of sense, the affection of the nervous tissue may be spoken of as a sensory 

 impulse; but after the affection has traversed the central organ and become modified 

 it is no longer a simple sensory impulse. We must then either call it a sensation 

 irrespective of whether any change of consciousness intervenes or no, or we must 

 give it a new name. Not wishing to introduce a new name, we have ventured to use 

 the word 'sensation' in a sense which neither affirms nor denies the coexistence of 

 consciousness. 



