18 MAX LEVINE 



is present, and the dispersion of the distribution is very great, as 

 indicated by a large coefficient of variability (26%). 



MacConkey Types I and II generally do not attack raffinose. The 

 few strains in these types which do, are not sufficient for comparative 

 purposes. Type IV tends to form more acid than Type III, but the 

 difference is not considered a reliable index for differentiation. 



There is no apparent relation between the animal source and the 

 amount of acid formed from raffinose. The mean for the sewage 

 strains, 1.11% normal acid, is higher than for those from other 

 sources. This difference, as was observed in the case of sucrose, is 

 due to the presence of the Voges-Proskauer-positive group among the 

 sewage strains. The mean for the Voges-Proskauer-negative strains 

 in sewage is 0.94% normal acid. 



The Voges-Proskauer-negative strains attack raffinose less readily 

 than do the Voges-Proskauer-positive strains. The means for the two 

 groups are 0.96 and 1.32% normal acid respectively, but the variability 

 among the strains is such as to make the difference (0.36) of question- 

 able significance. 



C. GLYCEROL 



The alcohol, glycerol, is attacked by many strains which form acid 

 but not gas. For calculating acid-production all strains which form 

 more than 0.4% normal acid in 72 hours at 37 C. are regarded as acid- 

 formers. The frequency distributions and the relation of quantitative 

 acid-production to the MacConkey types, to the source, and to the 

 Voges-Proskauer reaction are shown in Table 8. A sharp mode is 

 observed at 0.70% and the mean for all the strains is at 0.73% nor- 

 mal acid. 



The MacConkey types are indistinguishable on the basis of quan- 

 titative acid-production in 1% glycerol peptone solution altho Type III 

 tends to form somewhat less acid than the others. 



The differences between the means of organisms from the various 

 animal sources cannot be regarded as significant. The sheep strains 

 form the least amount of acid (0.60%- normal), while the means for 

 strains from other sources are, horse 0.67%, cow 0.71%, man 0.71%, 

 and pig 0.76% normal acid. The somewhat higher mean of the sew- 

 age strains (0.83%) is due, again, to the influence of Voges-Pros- 

 kauer-positive strains. These eliminated, the mean for the Voges- 

 Proskauer-negative strains in sewage is 0.70% normal. 



