BIOLOGICAL VAKIATIONS OF BACTERIA 



397 



index of proteolytic activities. To control the possible effect 

 of the acid production of B. coli, upon proteolysis, three of the 

 sugars, namely, glucose, lactose, and saccharose, had 1 per cent 

 of calcium carbonate added to neutralize any acid formed. An- 

 other control was also carried along, a stock strain of Sp. cholerae, 

 which produces but a shght amount of acid as compared with 

 B. coli, but, on the other hand, gives a marked amount of indol. 

 Seven different sugars were used besides the three containing 

 calcium carbonate, making a total of ten inoculations for each 

 organism. The organisms were cultivated in the respective 

 sugar peptone solutions for six days, at which time small amounts 

 of the cultures were poured over into fresh media for the con- 

 tinuance of the experiment, and then the Salkowski's test was 

 apphed to the original culture. After the seventh inoculation, 

 when all the strains gave negative indol tests, experiments for 

 reversions were begun, by transfering a small quantity of each 

 of the cultures into plain peptone, and proceeding with the test 

 as before. 



TABLE X 



Showing the effect of various carbohydrates upon the proteolytic activities of seven different 

 strains of B. coli, and one of Sp. cholerae, as evidenced by the indol test 



TABLE XL 



Results oj the indol tests in the experiments on reversion. * = Positive test obtained with 

 H2S0i only, f = Positive test obtained only after the addition oj nitrite 



