RESEARCHES ON CERTAIN PROBLEMS OF PLAGUE IMMUNITY 13 



TABLE L— Toxin 15. 



Filtrate from a 2 month's growth on Neutral Broth. 

 Test on Mice of 20-25 grammes weight. 

 Subcutaneous injection. 



TABLE IL— Toxin 16. 



Filtrate from 2 month's growth of the same bacillus and on the same broth as 

 Toxin 15. In this case the broth was made alkaline, 7 c.c. of normal caustic 

 soda per litre being added after the neutral point to litmus was reached. 



Test on Mice of 20-25 grammes weight. 



Subcutaneous injection. 



It was observed that the addition to the broth of i : 4 to i : 8 of 

 normal horse serum heated to 65° C, gave a very abundant growth, in 

 some cases with pellicle formation, but so far as this was investigated no 

 increase in toxin formation could be demonstrated. 



The cultures were grown for the most part in large flat bottles each 

 containing i to ij litres, but Erlenmeyer's flasks, with a thin layer of 

 medium in the flask, were also employed. Previous experience had 



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