MAX LEVINE 



may be made on the other types. It is therefore apparent that quanti- 

 tative acid-production in glucose is not a reliable criterion for differen- 

 tiation of the MacConkey types. 



There are many irregularities in the frequency distributions of 

 organisms from different sources with respect to acid-production in 

 glucose. The organisms from horse and man group themselves in a 

 manner simulating a normal distribution, but the frequency curves of 

 those from cow, sheep, and pig, contain 2 modes. These multiple 

 modes are probably due to the choice of classes and to the small num- 

 ber of cultures from each source. In the other test substances mul- 

 tiple modes are very infrequent. In the column headed "Mode," in 

 the frequency tables, the primary mode is recorded. 



The distribution of organisms from the sheep is interesting. Two 

 distinct groups are indicated, one of which generally produces more 

 than 2% normal acid and the other usually less than 1%. Of the 5 

 low-acid-formers, 4 are from a single animal (all the cultures obtained 

 from that animal), and they are distinguished morphologically from 

 all the other sheep strains in that they are distinctly longer. 



Among the sewage strains 2 well-defined modes are evident, at 

 1.9% ana 1.5% normal acid, corresponding with the modes of the 

 Voges-Proskauer-negative and the Voges-Proskauer-positive organ- 

 isms respectively. 



In a consideration of the different animal sources it appears that 

 the average amount of acid formed from glucose by Bacillus-coli-like 

 organisms from horse (2.03%) is greater than the amounts formed 

 by strains from pig, sheep and cow (1.70, 1.76, and 1.79%), while 

 the amount formed by human strains is intermediate (1.91% normal). 

 This relationship does not hold for other test substances and there 

 does not seem to be any marked relation between the quantities of acid 

 produced from glucose, and those formed from other fermentable 

 carbohydrates or alcohols by colon-bacillus-like organisms from the 

 animals recorded here. 



Quantitative acid-formation is better correlated with the Voges- 

 Proskauer reaction than with the source or with MacConkey's groups. 

 The Voges-Proskauer-negative organisms give an average of 1.82% 

 normal acid, with a mode at 1.90%, while the Voges-Proskauer-posi- 

 tive strains 1.46%, with a mode at 1.50% normal, and, altho the dif- 

 ference, 0.36, is probably not sufficient for reliable differentiation, it 

 is nevertheless significant, because rather striking differences in acid- 

 formation between the Voges-Proskauer-positive and the Voges-Pros- 



