PREFACE TO THE GERMAN EDITION. vii 



metabolism, especially its two main phases, anabolism and catabolism^ 

 It has been shown that the substances obtained by immunization 

 are nothing but the tools of normal cell-life, tools which we can thus 

 isolate from their place of production and subject to an individual 

 examination. This at once opens new paths for approaching the 

 study of vital phenomena, which embraces not only the physiology 

 and pathology of metabolism, but also certain other physiological 

 problems such as those of secretion, heredity, etc. 



At the recent Congress for Hygiene and Demography (Brussels), 

 in which the chief problems of immunity were discussed, it was seen 

 that my theory is not yet accepted by all the workers in this subject, 

 there being still a few opponents. This was to be expected. Cer- 

 tainly nothing is more desirable in all scientific problems than the 

 expression of different opinions, for as a result of experimental studies 

 they lead to a deeper insight into the subject in question. Hence 

 it is largely the opposition of Bordet and other distinguished 

 workers in the Pasteur Institute that has spurred us on in our experi- 

 mental labors, and caused us to establish the amboceptor theory 

 more firmly than ever. 



On the other hand it is very annoying when such authors as Gruber, 

 who have absolutely no personal experience in the main questions, 

 wage a bitter war merely because they have made a few literary 

 studies; it is the more exasperating since they seek to make up the 

 deficiencies in their arguments by the intensity and personality 

 of their attacks. Such authors are in no position to correctly orientate 

 themselves in the mass of true and false observations that each day's 

 literature brings forth. 



It was a great pleasure, therefore, to see one of the founders of 

 the doctrine of immunity, R. Pfeiffer, and that distinguished repre- 

 sentative of Paltauf's Institute in Vienna, R. Kraus, express them- 

 selves in favor of my theory. They confessed they had both really 

 opposed the theory from the start, and that the main purpose in devis- 

 ing their various experiments had been to show that it was untenable. 

 Just these, however, had convinced them that the side-chain theory 

 not only afforded the best explanation for their results, but had even 

 enabled them to predict these results. The chief problems now 

 under discussion are : (1) the constitution of active cytotoxic sub- 



