344: THE BIOLOGICAL SCIENCES AND MEDICINE. 



we owe both the spiritualistic and the materialistic phi- 

 losophies 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 philosophy was the fmit. And, as the course of his 

 speculations led him to establish an absolute distinction 

 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 func- 

 tion 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 prin- 

 cipal 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 ma- 

 chine which moves of itself) when it is wound up and 

 has, in itself, the physical principle of the movements 

 which the mechanism is adapted to perform, differs from 

 the same watch, or other machine, when it is broken, 

 and the physical principle of its movement no longer 

 exists. All the actions which are common to us and 

 the lower animals depend only on the conformation of 

 our organs, and the course which the animal spirits take 

 in the brain, the nerves, and the muscles ; in the same 



