RESEARCHES ON CERTAIN PROBLEMS OF PLAGUE IMMUNITY II 



It is unnecessary here to go more minutely into the results obtained 

 on animals, or the advantages claimed for the use of this material. 

 From our present standpoint, however, the toxity of the substance is of 

 interest. 



(i) It kills a large percentage of mice within 20-24 hours in doses 

 of I - 5 milligrammes. 



(2) Prepared from acute cases, it kills 15 -25% of half-grown white 

 rats in doses of 5-8 milligrammes ; prepared from sub-acute cases, 

 10-12 milligrammes are required to produce a fatal effect. 



(3) 20 milligrammes fail to kill a guinea-pig of 200 - 300 grammes 

 weight. 



Klein holds that the effects produced by the substance are due not 

 merely to the bacilli contained in the material, but depend largely on the 

 presence in the necrotic area of a " tissue toxin." 



Besredka (1905 and 1906) has proposed a new method for the 

 preparation of typhoid and plague endotoxins. 



The growth from an agar culture of B. pestis is emulsified, heated 

 to 60° C. for one hour, and then dried in vacuo. The lethal dose for the 

 mouse of this dried substance, injected subcutaneously, is five decimilli- 

 grammes. To obtain the plague endotoxin in the soluble state, the 

 dried bacilli are put in normal salt solution and horse serum in fixed 

 quantities. The mixture is placed in the ice-safe overnight, and is 

 centrifugalised on the following day. The clear supernatant fluid 

 contains the endotoxin, and the deposit of a sticky consistence is formed 

 of atoxic plague bacilli. 



The soluble endotoxin is highly toxic for the mouse, e.g., 0*02 centi- 

 gramme of dried bacilli, to which i c.c. of physiological salt solution 

 and 4 c.c. of horse serum have been added, corresponds to about 20 

 lethal doses of endotoxin. 



The plague endotoxin keeps for months in the ice-safe. It is 

 thermostable; heating to 55° C. for one hour leaves it intact; it is 

 slightly attenuated by heating for one hour to 65° C, but it is not 

 destroyed by heating to 57° C. for 15, or even 24 hours. 



Its essential characteristic, according to Besredka, is that its action is 

 neutralised by anti-plague serum. 



Besredka also investigated the endotoxin of the typhoid bacillus, and 



(121) 



