A HISTORY OF SCIENCE 



his ideas of philosophy and science. Then, in his 

 Discourse Touching the Method of Using One's Reason 

 Rightly and of Seeking Scientific Truth, he pointed out 

 the way of seeking after truth. His central idea in 

 this was to emphasize the importance of doubt, and 

 avoidance of accepting as truth anything that does 

 not admit of absolute and unqualified proof. In reach- 

 ing these conclusions he had before him the striking 

 examples of scientific deductions by Galileo, and more 

 recently the discovery of the circulation of the blood 

 by Harvey. This last came as a revelation to scien- 

 tists, reducing this seemingly occult process, as it did, 

 to the field of mechanical phenomena. The same me- 

 chanical laws that governed the heavenly bodies, as 

 shown by Galileo, governed the action of the human 

 heart, and, for aught any one knew, every part of the 

 body, and even the mind itself. 



Having once conceived this idea, Descartes began 

 a series of dissections and experiments upon the lower 

 animals, to find, if possible, further proof of this gen- 

 eral law. To him the human body was simply a ma- 

 chine, a complicated mechanism, whose functions were 

 controlled just as any other piece of machinery. He 

 compared the human body to complicated machinery 

 run by water-falls and complicated pipes. " The nerves 

 of the machine which I am describing," he says, "may 

 very well be compared to the pipes of these water- 

 works ; its muscles and its tendons to the other various 

 engines and springs which seem to move them ; its ani- 

 mal spirits to the water which impels them, of which 

 the heart is the fountain; while the cavities of the 

 brain are the central office. Moreover, respiration 



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