160 INFECTIONS OF THE DIGESTIVE TRACT 



soluble poisons diffusing readily from the bodies of the 

 bacteria, the typhoid bacilli hold their poisons tena- 

 ciously in their bodies, and that these endotoxins may 

 be liberated in the body of the host, when the bacterial 

 bodies are dissolved, but are not so liberated in ordinary 

 culture media. A more adequate hypothesis was formu- 

 lated by Professor Welch. According to this, the typhoid 

 bacilli are stimulated in the body by means of its defen- 

 sive juices to form and liberate their poisons. Such a 

 stimulus being wholly lacking in artificial culture media, 

 where their existence is not actively threatened, the 

 bacilli are not forced to make their poisons. It may be 

 that the difference in the poisons formed in the body 

 and in culture media is mainly one of quantity rather 

 than of kind. There is at least some ground for think- 

 ing that the character of the immunity is the same, 

 whether the poison comes from the bodies of bacteria 

 in culture or from similar bacteria under the stimulus 

 of the protective juices of an animal. 



The word "aggressins" has been introduced by Kruse 

 and Oscar Bail 1 to designate substances of unknown 

 constitution which are formed by most pathogenic 

 bacteria when in antagonism with the animal organism, 

 as for example when introduced into the peritoneal 

 cavity of a guinea-pig substances which break down in 

 some way the natural defenses of the body, so that the 

 bacterial invaders, previously held in check, become 

 reproductively and invasively active. The "aggressins" 



1 " Untersuchungen liber Typhus und Cholera Immunitat," 

 Archiv /. Hyg., lii, p. 272, 1905. 



