THE PRODUCTION OF ACTIVE IMMUNITY 151 



immunized with the residue and subsequently inoculated 

 with a large amount of the living germ, we obtain evidence 

 of hypothermia at a much earlier period, owing to the 

 fact that bacteriolysis takes place very rapidly since the 

 bacteriolytic substance is present in a form available 

 for immediate use. If, however, the amount of this sub- 

 stance directly available is not sufficient to cause death 

 and bacteriolysis of all germs present, those bacilli which 

 remain are still capable of further reproduction. The same 

 mechanism which causes destruction of the bacteria in 

 normal animals, and which is probably connected with 

 the phenomenon of phagocytosis is, however, still operative 

 in the immune animal. Thus we shall have two influences 

 at work in the immune animal to cause bacteriolysis, one 

 acting rapidly, and the other manifesting its action only 

 after a considerable interval of time. We should there- 

 fore expect theoretically that we would find in the im- 

 munized animal a marked fall in temperature at an early 

 time, due to the setting free of the poison from the bodies 

 of the bacteria disintegrated by the directly available 

 bacteriolytic substance followed by a secondary rise, and 

 a succeeding fall due to the liberation of the poison by 

 means of the factors present in the normal animal. How- 

 ever, this is not actually the case, since the effect of the 

 poison liberated at first has not worn off before the second 

 period of bacteriolysis becomes well established. Conse- 

 quently, the intermediate rise of temperature is absent. 



The results which follow the injection of the dead bac- 

 terial substance into animals immunized with the residue 

 are very interesting. As has been previously mentioned, 

 whereas animals treated with the residue develop an active 

 immunity to colon infection, they do not possess any greater 

 degree of tolerance for the colon poison than do untreated 

 animals. This is shown by the fact that the fatal dose of 

 the soluble poison is the same for the treated pig as for the 

 untreated control. This w^ould lead to the belief that the 

 immunity obtained to the living colon bacillus is, in the 

 case of the residue animals, purely a bacteriolytic one. If 



