624 



CHAPTER IV. 



Theory of Digestion, Sanguification, Coagulation, 

 Secretion, Nutrition, Muscular Motion, Sensa- 

 tion, fyc. 



" The idea of vital forces may gradually become so clear and 

 definite as to be available in science, and future generations may 

 include in their physiology propositions elevated as far above the 

 circulation of the blood, as the doctrine of universal gravitation 

 goes beyond the explanation of planetary motion by epicycles." 



WHEWELL. 



IN accordance with the prevalent doctrine of the 

 schools, Dr. Prout maintains, that " the true and 

 legitimate object of inquiry for the Physiologist 

 ought to be, not ivhat the vital principle is, but 

 what it does, just as the laws and effects of gra- 

 vitation are legitimate objects of inquiry, though 

 we know nothing, and probably never will know 

 any thing of the principle of gravitation." (Ap- 

 plication of Chemistry to Physiology.) Such, 

 however, was not the opinion of Sir Isaac New- 

 ton, who made repeated efforts to ascertain the 

 cause of gravitation, cohesion, chemical affinity, 

 and animal motion, all of which he referred to one 

 and the same cause. Yet it is maintained by Ber- 

 zelius, Tiedemann, Muller, Liebig, and more than 

 a hundred other physiologists of the nineteenth 

 century, that " the vital principle is a power 



