360 BIOLOGICAL SCIENCES AND MEDICINE xiv 



movements which the mechanism is adapted to 

 perform, differs from the same watch, or other 

 machine, when it is broken, and tlie 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 consciousness, by physical reasonings. To 

 a mind turned in this direction, Harvey's exposi- 

 tion of the heart and vessels as a hydraulic mechan- 

 ism must have been supremely welcome. 



Descartes was not a mere philosophical theorist, 

 but a hardworking dissector and experimenter, 

 and he held the strongest opinion respecting the 

 practical value of the new conception which he 

 was introducing. He speaks of the importance of 

 preserving health, and of the dependence of the 

 mind on the body being so close that, perhaps, the 

 only way of making men wiser and better than 

 they are, is to be sought in medical science. " It 

 is true," says he, " that as medicine is now practised 

 it contains little that is very useful; but without 

 any desire to depreciate, I am sure that there is 



