266 MAX LEVINE 



Sucrose and dulcitol therefore remain. These are the two char- 

 acters in regard to which there is considerable difference of 

 opinion among students of the B. coli group. MacConkey gives 

 preference to sucrose, and in this selection is supported by many 

 investigators (Howe 1912, Kligler 1915, Rogers 1915, etc.); 

 while Jackson (1911) and more recently Giltner (1916) subdivide 

 first on dulcitol. It is quite interesting, therefore, that on the 

 basis of the correlation coefficients there is really little choice 

 between the two. Both are equally well correlated with motility 

 (coefficient 0.53) ; partially with each other (coefficient 0.58) and 

 not associated with indol. Dulcitol correlates partially with 

 salicin (coefficient 0.60), while sucrose does not (coefficient 0.20). 

 On the other hand, sucrose is almost perfectly correlated with 

 raffinose (coefficient 0.99), whereas salicin is only partially (co- 

 efficient 0.58). Although neither can be regarded as associated 

 with glycerol, the coefficient with sucrose ( —0.38) is greater than 

 with dulcitol (-0.21). 



If our selection is to be guided entirely by correlation, the 

 choice between dulcitol and sucrose is a toss up. Sucrose was 

 finally selected for the primary division because it is more 

 widely distributed in nature, more available to students for 

 investigational purposes, more widely accepted by bacteriologists, 

 and its fermentation better correlated with the source than is 

 dulcitol decomposition. Differentiation on sucrose yields a 

 sucrose positive group of 93 strains, and a sucrose negative group 

 of 89 strains. 



THE SUCROSE NEGATIVE STRAINS OF THE COLI GROUP 



Of the 89 strains which did not form gas from sucrose, 33 

 (37.1 per cent) were positive in dulcitol; 69 (77.6 per cent) posi- 

 tive in glycerol; and 51 (57.3 per cent) gave gas in salicin; 53 

 (59.6 per cent) were motile; only 10 (11.3 per cent) failed to form 

 indoL 



The distribution of the organisms, with regard to motility, 

 dulcitol, glycerol, saHcin and indol is given in table 4, and the 

 coefficient of correlation for each pair of reactions is given in table 

 4a. For these strains motility is not distinctly correlated with 



