40 CRITICISM OF MECHANISTIC THEORY 



down into the muscles supplied by the 

 efferent nerves, distending them and thus 

 causing them to shorten. According to the 

 arrangement of nerve-fibres or tubes, and 

 valves, one form of reflex action or another 

 follows any given sensory stimulus. The 

 chief motive power for the whole of the 

 mechanisms by which Descartes suggested 

 that the human body is worked and develop 

 ment brought about was furnished by sup 

 posed rhythmical expansions of the blood in 

 the heart, owing to chemical explosions. 



The greater part of the physiology of 

 Descartes was extremely crude, and lacking 

 in experimental foundation. This crudeness 

 stands out in strong relief against the far 

 sounder, but at the same time far more 

 limited, observations and reasoning of Harvey, 

 whose writings had greatly influenced Des 

 cartes. Nevertheless the mechanistic ideas 

 first put forward in a thoroughly systematic 

 form by Descartes have continued to influ 

 ence biology up to the present day. 



If we trace the history of physiology on 

 wards from the time of Descartes we find 

 constant conflict between mechanistic and 



