x Preface 



regards as of fundamental importance for the comprehension of the 

 whole question of Immunity. I hope that after the appearance of 

 this treatise such oversights will not be so likely to occur. 



Should I not succeed in convincing my opponents of the justice 

 of the cause which I defend, I shall at least have informed my critics 

 and shall have given them an opportunity of discussing it with a 

 thorough knowledge of the material on which it is based. This 

 result alone would justify me in having undertaken this work. 



At first I intended to add to my explanation of Immunity a 

 theory of the phenomena of healing in infective diseases, but I soon 

 had to renounce this project, for its execution would have increased 

 too greatly the bulk of the book which, without it, has already assumed 

 considerable proportions. It seemed to me preferable to set forth 

 the present state of the question without paying too much attention 

 to the historical sequence of the discoveries, and to reserve for a 

 special chapter, at the end of the work, a sketch of the history of our 

 knowledge on Immunity. 



Before I ask the reader to glance through this work, I should 

 mention that I have been heartily seconded in its preparation by many 

 of my friends and collaborators. I offer my most sincere thanks to 

 MM. Roux, Nocard, Massart, and J. Bordet, who kindly undertook 

 to read my manuscript throughout, or such parts of it as related to 

 their special subjects. For example, M. Nocard rendered me a 

 very great service by correcting the paragraphs of Chapter xv, 

 which treat of the vaccinations against epizootic diseases, and 

 M. Massart, by giving me his advice on the subject of immunity 

 in plants. 



I owe very special thanks to M. Mesnil, who has been good 

 enough to give me very effective help in the dry task of correcting 

 the manuscript and proofs. 



I beg MM. E. Re"my and L. Barneoud to accept my thanks for the 

 care they have bestowed on the execution of the illustrations in this 

 work. 



METCHNIKOFF. 



PARIS, INSTITUT PASTEUR, 

 3 October, 1901. 



