160 MR. DARWIN'S CRITICS v 



that the processes which go on in the one are just 

 like those which take place in the other. In the 

 dog, there can be no doubt that the ner.vous 

 matter which lies between the retina and the 

 muscles undergoes a series of changes, precisely 

 analogous to those which, in the man, give rise to 

 sensation, a train of thought, and volition. 



Whether this neurosis is accompanied by such 

 psychosis as ours it is impossible to say ; but 

 those who deny that the nervous changes, which, 

 in the dog, correspond with those which underlie 

 thought in a man, are accompanied by conscious- 

 ness, are equally bound to maintain that those 

 nervous changes in the dog, which correspond with 

 those which underlie sensation in a man, are also 

 unaccompanied by consciousness. In other words, 

 if there is no ground for believing that a dog thinks, 

 neither is there any for believing that he feels. 



As is well known, Descartes boldly faced this 

 dilemma, and maintained that all animals were 

 mere machines and entirely devoid of consciousness. 

 But he did not deny, nor can anyone deny, that in 

 this case they are reasoning machines, capable of 

 performing all those operations which are per- 

 formed by the nervous system of man when he 

 reasons. For even supposing that in man, and in 

 man only, psychosis is superadded to neurosis the 

 neurosis which is common to both man and animal 

 gives their reasoning processes a fundamental 

 unity. But Descartes' position is open to very 



