ABSTRACTS 



85 



P+H = 6.8 at 30°C. When P+H is less than 6.8, a solution is acid 

 and when greater it is alkaline to pure water. 



A study of a large number of cultures of streptococci seems to indi- 

 cate that two limiting zones of hydrogen-ion concentration are reached, 

 as may be seen in the table. 



These hydrogen-ion concentrations have been found to be fairly 

 constant and would probably be more definite if the values were de- 

 termined electrometrically. 



It seems evident from these results that streptococci reach more or less 

 definite hydrogen-ion concentrations, which fact may serve to help in 

 their classification. 



The difference in the limiting hydrogen-ion concentration has not 

 been correlated thus far with any other reactions, but it is rather strik- 

 ing that such a large percentage of the streptococci from cases of human 

 infection reach only the lower zone of limiting hydrogen-ion concentration. 



This difference among the streptococci, brought out by the hydrogen- 

 ion concentration, can not be shown accurately by titration methods, 

 since the titrable acidity depends upon the composition of the medium. 



The Value of Lactose Bile for the B. Coli Presumptive Test. John W. 



M. Bunker. 



The use of lactose bile media for the B. coli presumptive test has 

 met with criticism because of the difficulty of obtaining fresh whole 

 bile whenever and wherever needed. It has been mainta,ined by some 

 investigators that the use of lactose broth without bile is as efficient 

 as the bile medium. Others have advanced the view that the inhibitive 

 action of bile is so great that with its use weak forms of B. coli are lost. 



The use of dried bile in the form known as Bacto Oxgall in 10 per 

 cent solution has given results always as satisfactory as those obtained 

 when preparing the medium from new whole bile, in tests upon oysters, 

 milk, cream, ice cream, polluted water, and sewage. 



When used in a 5 per cent solution dried bile has provided a medium 

 which detects B. coli by fermentation in higher dilutions occasionally 

 than when 10 per cent solution or Standard Lactose Bile is employed. 

 The 5 per cent solution has never failed to show fermentation in equally 

 high dilutions as the 10 per cent solution or the Standard medium. 



A water to which was added a small quantity of B. coli culture when 

 stored for a long time and tested daily with whole bile medium, ten 



