PREFACE 



FOR the past twenty years the science of immunity has been one of 

 the most progressive and most active branches in the department of 

 medicine. An enormous literature has accumulated; many new terms 

 have been coined, and numerous theories have been adduced; indeed, 

 the subject has acquired an aspect of complexity that is confusing to 

 those not specially interested or engaged in this work. 



The purpose of this book is a threefold one, namely : 



1 . To give to practitioners and students of medicine a connected and con- 

 cise account of our present knowledge regarding the manner in which the 

 body may become infected, and the method, in turn, by which the organism 

 serves to protect itself against infection, or strives to overcome the infection 

 if it should occur, and also to present a practical application of this 

 knowledge to the diagnosis, prevention, and treatment of disease. 



2. To give to physicians engaged in laboratory work and special workers 

 in this field a book to serve as a guide to the various immunologic methods. 



3. To outline a laboratory course in experimental infection and im- 

 munity for students of medicine and those especially interested in these 

 branches. 



1. The subject of infection is intimately connected with that of 

 immunity, and this is especially emphasized in those diseases for which 

 a specific therapy exists, for a knowledge of the nature of the infection 

 is of paramount importance in controlling the dosage and indicating the 

 method of administration of a specific therapeutic agent. By describing 

 principles and technic with considerable detail, a special effort has been 

 made to render Part IV of this book of particular value to practitioners 

 of medicine. 



The day is past when the physician and surgeon can relegate the things 

 of immunity entirely to the laboratory. Diagnostic methods and re- 

 actions and the field of specific therapy, vaccine, serum, and chemo-, 

 are subjects of such practical importance that it is obvious that the 

 physician and the student of medicine can no longer be merely mildly 

 interested onlookers. The physician who injects salvarsan, a serum, 

 or a vaccine, or who uses a diagnostic reaction, must be prepared to ex- 

 plain to his patient the nature of the therapy he employs and the sig- 



