SEVENTEENTH AND EIGHTEENTH CENTURIES 153 

 assumed to take place in muscular contraction, which, indeed, occurs as the 

 result of impulse from the nervous system — that is to say, through fluid 

 flowing to it from without. Here obviously comes in Descartes's theory of 

 the currents in the nerves; on the basis of this theory Borelli concludes that 

 the swelling of the muscles upon contraction is caused by a process of fer- 

 mentation, which arises when the blood in the muscles is mixed with the 

 nervous fluid flowing into it. For the fact that Borelli was unable, with the 

 means available at that time, to explain the extremely involved co-operation 

 of physical and chemical processes which constitute muscular contraction, 

 he cannot, however, be blamed; on the contrary, his assumption that a 

 complicated chemical action and not a simple mechanical one is here in- 

 volved must be admitted to be an inspired presentiment of what our modern 

 science has at last definitely established. After having then given an account 

 of a thorough investigation of the muscular mechanism of the heart and the 

 respiratory system, Borelli concludes his work with some speculations on 

 the subjects of digestion and fertilization, which are partly based upon the 

 opinions of his precursors and are otherwise not very successful, so that they 

 may be passed over here. The same is true of his purely medical speculations, 

 such as his theory that fevers do not originate in the blood, but in the nerv- 

 ous fluid, and other assumptions in connexion therewith. 



Borelli creates experimental biology 

 Borelli was above all a mechanician and his greatness lies in his having 

 created experimental biology operating with purely mechanical forces. In 

 the introduction to his work, it is true, he gives the assurance that all the 

 mechanical phenomena in the living body, which he proceeds to describe, 

 are produced by the vital spirit — had he not admitted this, he would cer- 

 tainly never have obtained the papal authority to publish his work, which 

 now adorns the first page of his book — but having once made this theoreti- 

 cal reservation, he carefully avoids in the discussion that follows the inclusion 

 of any other points than the purely mechanical. And it is just for this reason 

 that, in spite of occasional weaknesses, his work stands out as the first to 

 apply all through the fundamental principle on which modern biology is 

 based. 



Borelli was highly appreciated by his own and the succeeding age; thus, 

 the great Dutch physician Boerhaave advises every doctor to read the work 

 De motu animalium. Although he was certainly the foremost, he was not 

 the only scientist of his kind to tackle biological problems from a purely me- 

 chanical point of view. Of those of his contemporaries who distinguished 

 themselves in this respect two in particular are worthy of a detailed account. 



Claude Perrault was born in Paris in 161 3, the son of a lawyer. He 

 studied at the university there; first of all, mathematics and the classical 

 languages, and then chemistry. Having taken a doctor's degree he practised 



