RESEARCHES ON CERTAIN PROBLEMS OF PLAGUE IMMUNITY 19 



lethal dose had risen from the O'l c.c. of the Table to 0*8 c.c. Higher 

 temperatures, as might be expected, cause similar deterioration in a much 

 shorter time. The effect of exposing the toxin to a temperature of 

 70" C. is shown below : — 



TABLE XL 

 Showing influence of heat to 70° C. on Toxin No. 10. 



Where irregularities occur, such as are frequent in the testing of 

 plague toxin, it is extremely difficult to trace the influence of the 

 virulence of the race of bacillus on the toxicity. It was found impossible 

 to establish any definite relation between virulence and toxicity, but a 

 strong impression was formed that as a culture diminished in virulence 

 the filtrate obtained from it became less toxic. 



Incubation Period. — The incubation period lasts from 6 to 24 hours 

 according to amount of toxin injected. In certain cases, where very old 

 cultures are used, convulsions occur almost immediately after the injection, 

 but these are probably due to the presence of cadaverin, as has been 

 suggested by Kolle. These frequently pass off in a short time to be 

 succeeded by the symptoms of toxic action. 



Effects and Symptoms resulting from the Injection of Toxin. — If the 

 injection is subcutaneous, within 24 hours a soft oedematous swelling, 

 often very extensive, is observed in the vicinity of the site of inoculation. 



(129) K 



