52 CROONIAN LECTURES 



those sciences into which the idea of life does 

 not enter. 



As the second stage of ideas in the abiolo- 

 gical sciences consisted in the assumption of an 

 imponderable matter, which was considered to 

 be separable from the ponderable matter, and 

 diffusible through it, giving rise to the phe- 

 nomena of force in every part ; so the second 

 stage, or partial separation in the ideas of 

 living force and matter, is marked by the 

 assumption of a living imponderable gas or 

 fluid pervading the ponderable matter. 



This stage, from the renown of him who gave 

 it the greatest support in England, may well be 

 called the fiunterian stage. 



Even Asclepiades and Galen spoke of a 

 subtle humour or spirit existing in the body, 

 which they compared to air. 



The chemical tendencies of the seventeenth 

 century led to the supposition that it was 

 sulphureous or nitrous acid ; and, soon after- 

 wards, it was compared to an aether. Even 

 Newton, in the twenty-third query, says : " Is 

 not vision performed by the vibrations of this 

 medium aether at the bottom of the eye, propa- 

 gated by the solid capillamenta of the nerves 



