230 Science Religion and Reality 



chemical changes rather than governing and controlling them. 

 Illness resulted from the overthrowing of one or more of the archaei, 

 so that chemical changes could pursue their courses unchecked. 

 This distinction is important historically because researches on the 

 phenomena of autolysis have shown that after death in surviving 

 organs enzyme actions proceed uncontrolled until complete dis- 

 integration of the tissue may occur, and this quite distinguished 

 from the action of bacteria, as in putrefaction. Thus van 

 Helmont's notion that chemical processes in the body are withstood 

 by archaei was an interesting forerunner of the modern view that 

 they are limited by the laws of mass action and other chemical 

 necessities. 



But a mechanistic influence of enormous importance was at 

 hand in the shape of Rene Descartes^ who in 1 664 published the 

 first scientific textbook of mechanistic physiology, the " Traite de 

 I'Homme." Descartes' philosophy in so far as it bore upon 

 physiology was an absolute dualism. He argued strongly for the 

 immateriality of the soul, and at the same time applied the most 

 rigid mechanistic principles to the body. The seat of interaction 

 he placed in the pineal gland, an anatomical structure situated over 

 the brain and now known to be a vestigial eye. He completed 

 finally the separation between the vital principle and the thinking 

 principle by placing the latter in the mind and giving up the vegeta- 

 tive functions entirely to the body and hence to deterministic 

 mechanism. It followed from his theories, though he did not 

 carry them as far as they logically would go, that animals, possessing 

 no soul, were absolutely and completely mechanistic in their 

 operation. 



No philosopher has ever exercised so great an influence on 

 purely scientific studies as has Descartes. He influenced the last 

 of the iatro-chemists on the one hand and the first of the iatro- 

 physicists on the other. Franciscus Sylvius of Leyden headed the 

 first mechanistic movement in biochemistry, and wrote in defence 

 of mechanistic notions, accepting all van Helmont's chemistry 

 but rejecting his doctrine of archaei. It is to this Sylvius that we 

 owe the differentiation between acids and alkalies and the building 

 of the first University Chemical Laboratory. 



In two other directions did Descartes' mechanistic influence 

 extend itself to great effect. Nicholas Stensen, who discovered 

 that the heart was a muscular organ, and early fellows of the Royal 



