ADAPTATION 207 



It is impossible to say here l more than a few words 

 about the phenomena and the theory of immunity proper, 

 which have attained the dimensions of a separate science. 

 Let me only mark those general points which are of 

 the greatest theoretical interest. Discoveries of the most 

 recent years have shown not only that against the " toxins ' 

 of bacteria, snakes, and some plants, the organism is able 

 actively to produce so-called " anti-toxins " that is, soluble 

 substances which react with the toxins and destroy their 

 poisonous character whenever required, but that against 

 any foreign body of the albumen group a specific reaction 

 may occur, resulting in the coagulation of that body. But 

 the destruction of the noxious substance or foreign albumen 

 actually present is not all that is accomplished by the 

 organism. " Acquired immunity ' proper, that is, security 

 against the noxious material for a more or less extensive 

 period of the future, depends on something more. Not 

 only is there produced as much of the so-called " anti-body ' 

 as is necessary to combine with the noxious, or at least 

 foreign substances which are present, but more is produced 

 than is necessary in the actual case. On this over-pro- 

 duction depends all active immunity, whether natural or, 

 as in some kinds of vaccination, artificial ; and so-called 

 " passive " immunity, obtained by the transfusion of the 

 serum of an actively immune organism into another also 

 depends upon this feature. 2 



This phenomenon in particular the production of more 

 of the antitoxin or the " precipitin " than is actually 



1 See Jacoby, Immunitdt und Disposition, Wiesbaden, 1906. 



2 Collected Studies on Immunity by Ehrlicli and his Collaborators, trans- 

 lated by Ch. Bolduan, New York and London, 1906. 



