336 THE BIOLOGICAL SCIENCES AND MEDICINE. [LECT. 



the material and the mental worlds, he was logically 

 compelled to seek for the explanation of the pheno- 

 mena 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 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 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 way as the movement 

 of a watch is produced by nothing but the force of its 

 spring and the figure of its wheels and other parts. 



Descartes' " Treatise on Man " is a sketch of human 

 physiology, in which a bold attempt is made to explain 

 all the phenomena of life, except those of conscious- 

 ness, by physical reasonings. To a mind turned in 

 this direction, Harvey's exposition of the heart and 



