RESEARCHES ON CERTAIN PROBLEMS OF PLAGUE IMMUNITY 1 5 



TABLE IV.— Toxin 13. 



Filtrate from 2 month's growth on same Neutral Broth as No. 7. 

 Test on Mice 15-20 grammes weight. 

 Subcutaneous injection. 



It thus appears that the maximum toxicity of the culture is syn- 

 chronous with the period when most of the organisms have undergone 

 degenerative changes or have died ; it seems probable, therefore, that the 

 toxic substances have been set free as the result of a process of autolysis. 

 Reference will be made to this in discussing the question of toxins. 

 Most of the filtrates tested were from cultures 8 to 10 weeks old. 



Great variations were observed in the toxicity of the filtrates from 

 different brews of bouillon made by the same methods and with the 

 same proportions of the components. Similar inexplicable variations are 

 well known in the preparation of diphtheria and tetanus toxin. 



It would be impossible here to give the protocols of all the tests 

 carried out in ascertaining the toxicity of different filtrates, but those 

 recorded are typical of the results obtained in the case of the more toxic 

 filtrates. A number examined were found to be much less toxic than 

 Toxin No. 10. As this toxin was employed for a test toxin in testing 

 the sera, the protocols of tests on mice and rats are given (Tables V., 

 VI., VII. and VIII). It will be noted that there is a certain amount of 

 irregularity in the results on mice, which makes the determination of 

 the minimal lethal dose a matter of some difficulty. 



(•25) 



