154 



WINSLOW, ROTHBERG AND PARSONS 



duction in dehydrated broth). The average reactions for these 

 groups after various periods of incubation are indicated below. 

 The 116 cultures which ultimately became acid in both cases 

 (class A) changed more slowly in the peptone medium, either 

 because of its greater initial alkalinity, greater buffer action, or 

 lower nutritive value, but by the fifth day at 30° they reached 

 about the same point. Members of class B changed more slowly 

 in the dehydrated medium than did those of class A but reached 

 the same final end point, while in the peptone medium they never 

 passed beyond the neutral point. Class C behaved like class B 

 in the dehydrated medium, but in the peptone medium showed no 



TABLE 2 

 Average pH values in dehydrated and peptone media 



change. Class D and class E showed no change in the peptone 

 medium but slight, transitory or permanent, production of alkali 

 in the dehydrated medium. In view of the difficulty in making 

 accurate readings over 6.8 these last two groups may best be 

 considered as one. 



We may therefore consider the strains studied by us as divided 

 into two main groups, Classes A, B and C which strongly acidify 

 the dehydrated broth and classes D and E which fail to form 

 acid in either medium. The first group, however, includes 116 

 strains which show an equally strong acid production in the pep- 

 tone broth, 29 which show a slower acid production in the pep- 

 tone broth and 8 which show no change in peptone broth. 



It appears evident that we are dealing here with a group of 

 organisms which generally attacks glucose but which contains a 



