CLASSIFICATION OF ACIDURIC BACTERIA 



417 



broth, with and without the addition of blood. Grown in 

 unneutraHzed glucose broth, some strains produced an acidity 

 of plus seven after five days incubation. I was unable to detect 

 gas even when blood was added to the medium. Anaerobic 

 milk cultures gave irregular results. Some cultures clotted the 

 milk in periods ranging from eight to fifteen days, giving rise to 

 an acidity that did not go beyond plus 7. In other instances 

 the organisms failed to grow. 



The figures in the table below represent the increase in acidity 

 in puncture cultures in 0.5 per cent agar containing 1 per cent 

 of the various test substances. The incubation period was five 

 days. 



TABLE 4 

 B. bifidus. Increase in acidity in 0.5 -per cent agar after five days at 37° 



In the latter part of this experiment the process of sugar free- 

 ing the broth used in the preparation of the medium was carried 

 beyond the usual stage to determine whether the products result- 

 ing from the greater development of B. coli served to enrich the 

 agar. Table 5 shows the results of comparative tests of half 

 per cent agar, one lot of which was subjected to more extensive 

 proteolysis by B. coli than the other. A distinct cloudiness 

 accompanied the increased acid production. It is evident that 

 the earlier cessation of growth in some lots of medium is due, 



