in] of the New Physics. 61 



"serve as the organs of the external senses, and finally 

 "distending the muscles give movement to all the limbs." 



What I have just quoted is enough to shew that Descartes 

 was not a physiological inquirer. His method in physiology 

 was not that of Harvey, not that which since Harvey's time has 

 continued to bring in a rich harvest of discovered truth, not 

 that of working one's way by careful observation, and patient 

 experiment or trial, out of exactly determined anatomical facts, 

 up to the real meaning of the facts. He had a special purpose in 

 view, and with that in view took a freer, wider sweep. He had 

 to shew that the new views which were making it clear in so 

 surprising a way that the universe was a machine working in 

 accordance with physical laws, might be applied also to man ; 

 that man, that is to say the body of man, might also be regarded 

 as a machine working in accordance with physical laws. He 

 had to shew this with the help of the knowledge of the 

 time, and he achieved this by picking out such parts of the 

 anatomical discoveries of the age as suited his purpose, and by 

 weaving these together with many other statements, for which 

 he gives no authority and which he yet treats as accredited 

 truths, into a theory of the constitution and action of the 

 nervous system viewed as a mere machine. 



I shall have occasion in a later lecture to dwell on some of 

 the details of Descartes' theory of the working of the nervous 

 system, and to shew how he utilized the doctrine of the animal 

 spirits to explain the phenomena of sensation and movement. 

 For him, as we shall see, the animal spirits constituted a fluid, 

 a very subtle fluid it is true, but still a fluid amenable to the 

 physical laws governing fluids, and for him the nerves were tubes 

 along which the spirits flowed in a wholly mechanical manner. 

 In his exposition he makes assumptions, such as the presence 

 in the nerves of valvular arrangements, for which he gives no 

 . evidence and for which he had no authority. I do not enter 

 into these points now,^ only wish to call attention to his work 

 as an attempt to apply the new philosophy of exact mathematics 

 and physics to the interpretation of the phenomena of living 

 things. 



Descartes' contemporaries stumbled, as we now stumble, at 



