On Immunity tuith Special Reference to Cell Life. 425 



knowledge of infectious diseases during the past century. Schwann's 

 classical investigations must be regarded as the first link in the long 

 chain. Schwann it was who, in an unsually brilliant manner, first 

 demonstrated that the decomposition of organic bodies in the processes 

 of fermentation and putrefaction was never spontaneous, but con- 

 stantly arose through the agency of micro-organisms coming from 

 without. This line of investigation reached its zenith in the fundamen- 

 tal work of Pasteur, of which the first and the greatest result — Lister's 

 method of wound treatment— worked a revolution in surgery. Then 

 followed the profound investigations of Koch on Anthrax, and the 

 piu-e cultivation of the most important pathogenic bacteria. 



The work of Pasteur and of Koch aff'orded the first basis on which the 

 study of artificial immunity could be again undertaken. The possibility 

 of voluntarily producing a number of the most important infectious 

 diseases of men and animals, and of modifying at will pure cultiva- 

 tions of bacteria, either, according to Jenner's precedent, by passage 

 through the animal body, or otherwise in artificial culture media, 

 laid the foundation on which advancement could proceed. Pasteur 

 himself was the first, after Jenner, to produce an artificial immunity 

 by using an attenuated virus ; and he was also able to introduce the 

 procedure to some extent into practice with most beneficial results. 

 Still the theoretical explanations of all these facts lagged far behind 

 their practical efi'ects. The very able investigations of Metchnikofi" and 

 his theory of phagocytosis were, to many investigators, inconclusive. 



With Behring's discovery, that in the blood serum of animals immu- 

 nised against diphtheria and tetanus, there were contained bodies which 

 were able to specifically protect other animals against the toxines of 

 these diseases, an altogether new factor was introduced into the 

 question. This remarkable discovery seemed at one stroke to open 

 up an entirely new and extremely promising prospect of immunising 

 mankind against the majority of the infectious diseases. It was, 

 therefore, somewhat disappointing when there did not follow, on the 

 successful practical application of diphtheria antitoxic serum, a rapid 

 succession of similar achievements. It may with truth be said, that 

 during recent years there has been somewhat of a standstill in the 

 further following-out of a work at first so enthusiastically received. 

 By purely empirical methods, e.g., by the production and use of sera of 

 very great antitoxic value, the results attained showed no improve- 

 ment. Better success was only to be hoped for when by an accurate 

 knowledge of the theoretical considerations underlying the question 

 of immunity, explanations of the previous ill-success were forthcoming. 

 Impelled by these considerations I laboured for years trying to shed 

 some light into the darkness that shrouded the subject. 



In all exact work with chemical bodies — for only as such can we 

 regard the toxines produced by the living bacteria — the first desider- 



2 K 2 



