274 THE HUMAN MECHANISM 



same forefoot. We should certainly not expect a conscious 

 animal to do this ; for, after trying one plan of action a few 

 times, it would realize that its efforts were unavailing, and 

 would try something else, such as jumping away. This same 

 peculiarity is met with in all animals deprived of the cere- 

 brum. They act like mere complicated and faithful machines ; 

 they do not act as if they were thoughtful, original, or wise. 



Especially striking is the avoidance of objects during 

 locomotion. This fact looks at first sight as if the animal 

 were aware of the presence of the obstacle in its path ; but a 

 dog without a cerebrum, even when it has been without food 

 for a day or more, will go to one side of a piece of meat and 

 pass it by. He acts as if unaware of the nature of the object, 

 of its use as food, etc. The image of the piece of meat 

 formed on his retina seems to generate nervous impulses 

 which pass to the brain by way of the optic nerve and re- 

 flexly guide the movements of the dog, but these impulses 

 do not inform the animal of the nature of the object, and 

 we have no reason to believe that the dog is aware of the 

 existence of the meat. 



When we consider our own experience we find that we 

 too, as we walk along a crowded street, avoid objects, not 

 only without noticing them but without even being aware 

 of their presence. Here again the afferent impulses from 

 the retina pass to the nervous system and reflexly guide our 

 walking without affecting consciousness at all. And the 

 wonderful feats of somnambulism, where the " eyes are 

 open " but " their sense is shut," where the sleeper main- 

 tains his balance and avoids stumbling in situations where 

 he would almost inevitably fall if he were aware of his 

 surroundings, show how perfect is this very complicated 

 mechanism of locomotion, which seems to be complete even 

 in the absence of the cerebrum. 



We are, indeed, so accustomed to regard our actions as 

 volitional and conscious that we rarely consider the large 



