viii PREFACE TO THE FIRST EDITION. 



with such additions as would contribute to the 

 completeness of the work, they are now collected. 

 in larger type, in the present volume and under a 

 more suitable title. 



It was thought best to treat the subject broadly, 

 to begin with the fundamental principles of infec- 

 tion and resistance and to introduce the reader to 

 the more complex conceptions of the present time 

 by taking him briefly over the main historical and 

 developmental steps. 



It will be obvious that the views of Ehrlich, 

 concerning the production of antibodies, the nature 

 of the reactions into which the latter enter, and the 

 methods by which bacteria produce disease, have 

 been utilized extensively. This course demands no 

 justification, when it is appreciated that by no 

 other means can one at the present time correlate 

 a multitude of well-established facts which bear 

 on the problems of immunity. Whatever ma}'' be 

 the eventual fate of the side-chain theory and 

 certain phases of it carry the aspect of finality we 

 should appreciate as much as possible the extent to 

 which it has shaped modern thought, and recognize 

 that it has won jan imperishable place in the his- 

 tory of biologic progress. 



It should also be understood that the utilization 

 of the side-chain theory in no sense carries with it 

 a negation of the importance of phagocytosis, a 

 fact which is plainly set forth on pages 356-7. 

 Without doubt the role of the phagocytes in recov- 

 ery from a large group of infections is on a better 

 and truer basis than it has ever been before, and 

 for this condition the recent work on opsonins has 

 been most significant. 



