2 ! IMMUNE SERA 



we can distinguish several classes of organisms. 

 One class is characterized by the secretion of 

 highly toxic soluble substances, both in the living 

 body and in the culture fluid. The type of this 

 class is the diphtheria bacillus. Another class pro- 

 duces highly toxic substances, which instead of 

 being given off, remain within the body of the 

 bacterium. These poisons may be demonstrated 

 in old cultures in which a certain amount of dis- 

 solution (" autolysis ") has taken place, or they 

 may be obtained by mechanically breaking up the 

 bacteria by pressure and grinding. These sub- 

 stances are spoken of as endotoxins, and are liber- 

 ated in the body when the bacteria are disintegrated 

 by the bacteriolytic agencies. The type of this 

 class is the spirillum of cholera, an organism which 

 produces a powerful endotoxin and which very 

 readily undergoes bacteriolysis. In addition to 

 these two classes we know of a large number of 

 bacteria which neither secrete a highly toxic soluble 

 substance as do diphtheria bacilli nor disintegrate 

 as readily as the cholera spirilla, and which never- 

 theless are extremely pathogenic. Hiss has sug- 

 gested that many organisms, if not all, secrete sub- 

 stances which are not soluble in their condition 

 at secretion, but which are susceptible to digestion 

 in the animal body. These substances thus become 

 soluble and assimilable, and when toxic act harm- 

 fully on the body cells. Under ordinary circum- 



