q 
v 
160 MR. DARWIN’S CRITICS 
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 nervous 
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 ved ) 
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