XIV BIOLOGICAL SCIENCES AND MEDICINE 359 



tant does the subject seem to Descartes, that he 

 returns to it in the " Traite des Passions," and in 

 the " Traite de rHomme/^ 



It is easy to see that Harvey's work must have 

 had a pecuHar significance for the subtle thinker, 

 to whom we owe both the spiritualistic and the 

 materialistic philosophies of modern times. It was 

 in the very year of its publication, 1628, that 

 Descartes withdrew into that life of solitary 

 investigation and meditation of which his phi- 

 losophy was the fruit. And, as the course of his 

 speculations led him to establish an absolute dis- 

 tinction of nature between the material and the 

 mental worlds, he was logically compelled to seek 

 for the explanation of the phenomena of the 

 material world within itself; and having allotted 

 the realm of thought to the soul, to see nothing 

 but extension and motion in the rest of nature. 

 Descartes uses " thought " as the equivalent of our 

 modern term " consciousness." Thought is the 

 function of the soul, and its only function. Our 

 natural heat and all the movements of the body, 

 says he, do not depend on the soul. Death does 

 not take place from any fault of the soul, but only 

 because some of the principal parts of the body 

 become corrupted. The body" of a living man 

 differs from that of a dead man in the same way 

 as a watch or other automaton (that is to say, a 

 machine which moves of itself) when it is wound 



up and has, in itself, the physical principle of the 

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