PREFACE. 



WHEN", ten years ago, I was preparing my Lessons on the Compa- 

 rative Pathology of Inflammation for the press, I hoped that 

 the other sections of the phagocytic theory Immunity, Atrophies, 

 and Healing would soon follow this first work. This hope has not 

 been realised, and it has needed prolonged work ere I could publish 

 the volume I have just completed. 



During this long period I sent out several ballons d'essai under 

 the form of summaries of the question of Immunity, published in the 

 Semaine medicale (1892), the Ergebnisse of Lubarsch and Ostertag 

 (1886), and the Handbuch der Hygiene by Weyl (1897). I there 

 attempted, as far as possible, to give a general picture of the 

 phenomena of Immunity in the infective diseases, and it was my 

 desire to excite criticism and opposition, in order to determine the 

 fate of the theory of phagocytes in its application to the problem of 

 Immunity. 



The most recent attempt in this direction was made at the Inter- 

 national Congress at Paris, in the past year (1900), when I presented 

 my report on Immunity before an audience which included, amongst 

 others, my principal opponents. It was the result of this Congress 

 which at length decided me to bring together my vie^ * on Immunity 

 in a volume which I now present to the reader. 



Convinced that many of the objections raised against the phago- 

 cytic theory of Immunity proceeded solely from an insufficient 

 knowledge of the theory, I thought that a work condensed into one 

 volume might render some service to those who are interested in 

 the problem of Immunity. I do not know whether I shall convert my 

 opponents, but I am convinced that a perusal of this book will clear 

 away certain misunderstandings. A very competent observer recently 

 confessed in one of his publications that for many years he had 

 been unaware of the experiments of M. J. Bordet and myself on 

 Immunity against the cholera vibrio, experiments which he now 



