PREFACE. Xlll 



more as to their functions than we have learned 

 concerning vision from counting the surfaces on the 

 eye of the fly. The most beautiful and elevated 

 problem for the human intellect, the discovery of 

 the laws of vitality, cannot be resolved, nay, cannot 

 even be imagined, without an accurate knowledge 

 of chemical forces ; of those forces which do not act 

 at sensible distances ; which are manifested in the 

 same way as those ultimate causes by which the 

 vital phenomena are determined ; and which are 

 invariably found active, whenever dissimilar sub- 

 stances come into contact. 



Physiology, even in the present day, still endea- 

 vours, but always after the fashion of the phlogistic 

 chemists (that is, by the qiialitative method), to 

 apply chemical experience to the removal of diseased 

 conditions ; but with all these countless experi- 

 ments we are not one step nearer to the causes and 

 the essence of disease. 



Without proposing well-defined questions, experi- 

 menters have placed blood, urine, and all the consti- 

 tuents of the healthy or diseased frame, in contact 

 with acids, alkalies, and all sorts of chemical re- 

 agents ; and have drawn, from observation of the 

 changes thus produced, conclusions as to their 

 behaviour in the body. 



