THE VITAL IMPETUS 121 



reversible enzymes and kinases and the like, to realise 

 that the belief in a vital agency is an intuitive one, 

 and that the mechanistic conception of life is only 

 the result of the extension to biology of methods of 

 investigation, and not a legitimate conclusion from 

 their results. 



To the anatomist, the embryologist, and the natu- 

 ralist, as well as to the physicist unacquainted with 

 the details of physiology, no less than to the ordinary 

 person this is perhaps by far the most general attitude 

 of mind. It would probably be impossible for anyone 

 to study only organic form and habits and come to 

 any other conclusion than that there was something 

 immanent in the organism entirely different from the 

 agencies which, for instance, shape continents, or 

 deltas, or river valleys. And this conclusion would 

 probably come with still greater force to the embryo- 

 logist, even though he still possessed a general know- 

 ledge of physiological science. 



The mechanistic conception of life has, without 

 doubt, been the result of the success of a method of 

 analysis. One sees clearly that just in proportion as 

 physical and chemical sciences have been most prolific 

 of discovery, so physiology, leaning upon them and 

 borrowing their methods, has been most progressive 

 and mechanistic. 



Mechanistic hypotheses of the organism may all 

 be traced back to Descartes, who built upon the work 

 of Galileo and Harvey. The anatomy of Vesalius and 

 his successors would have led to no such notions, had 

 not the discoveries of Copernicus, Tycho, and Kepler 

 shown men an universe actuated by mechanical law. 

 To a thinker like Descartes, at once the very type 

 of philosopher and man of science, Harvey's discovery 

 of the circulation of the blood must have suggested 



