PREFACE. XXIX 



structure of the tissues cannot teach us their 

 uses ; and from the microscopical examination 

 of the most minute reticulations of the vessels 

 we can learn no more as to their functions than 

 we have learned concerning vision from count- 

 ing 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 mani- 

 fested in the same way as those ultimate causes 

 by which the vital phenomena are determined ; 

 and which are invariably found active, when- 

 ever dissimilar substances come into contact. 



Physiology, even in the present day, still 

 endeavors, but always after the fashion of the 

 phlogistic chemists (that is, by the qualitative 

 method), to apply chemical experience to the 

 removal of diseased conditions ; but with all 

 these countless experiments we are not one 

 step nearer to the causes and the essence of 

 disease. 



Without proposing well-defined questions, 

 experimenters have placed blood, urine, and 

 all the constituents of the healthy or diseased 

 frame, in contact with acids, alkalies, and all 

 sorts of chemical reagents; and have drawn, 

 c* 



