Chapter XV 



The Circulation of the Blood is Confirmed 

 by Plausible Methods 



IT WILL not be irrelevant here to point out 

 further that even according to common ideas, 

 the circulation is both convenient and necessary. 

 In the first place, since death is a dissolution re- 

 sulting from lack of heat, all living things being 

 warm, all dying things cold {Aristotle, De Respir.y 

 lib. 2 & jy De Part. Animal., etc.), there must be a 

 place of origin for this heat. On this hearth, as it 

 were, the original native fire, the warming power 

 of nature, is preserved. From this heat and life may 

 flow everywhere in the body, nourishment may come 

 from it, and on it all vegetative energy may depend. 



That the heart is this place and source of life, in 

 the manner just described, I hope no one will deny. 



The blood, then, must move, and in such a way 

 that it is brought back to the heart, for otherwise 

 it would become thick and immobile, as Aristotle 

 says {De Part. Animal., lib. 2), in the periphery 

 of the body, far from its source. We note that 

 motion always generates and preserves heat and 

 spirit, while in quietness they disappear. So the 

 blood, in the extremities, thickens from the cold 



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