PEEFACE 



TO THE FIEST EDITION. 



The author has become convinced, by several years' 

 intimate intercourse with students of medicine, that their 

 acquaintance with the subjects he has endeavored to in- 

 clude in this little volume would be facilitated, if the 

 views, which are now taught and scattered throughout 

 the often expensive works of their authors, were collected 

 in a convenient form for study and reference. Taking 

 it for granted that a knowledge of this subject is of fun- 

 . damental importance in its bearing upon the study of 

 physiology and pathology, and stimulated by the frequent 

 inquiries of students for an appropriate source of infor- 

 mation, he has prepared what he now submits to them. 



He has sought to obtain a continuous history of the 

 evolution of the " cell doctrine " up to its present state, 

 without embarrassing his pages with a large number of 

 isolated facts. He has attempted, however, to secure a 

 completeness, and to make the work useful to physicians 



