258 MAX LEVINE 



ously employed. It may be recalled that the differentiation of 

 the colon-intermediate-typhoid group on glucose and lactose 

 fermentation is strikingly correlated with pathogenicity. 



STATISTICAL STUDY 



In the following pages is evolved a classification of coli-like 

 bacteria based primarily upon correlated characters. The study 

 is made upon 333 organisms obtained from soil, sewage and the 

 feces of man, horse, sheep, pig and cow. 



The characters considered are the methyl-red and Voges- 

 Proskauer reactions, indol production, motility, gelatin liquefac- 

 tion and gas formation from sucrose, raffinose, dulcitol, glycerol, 

 salicin, dextrin, inulin and corn starch. Other fermentable 

 substances — lactose, maltose, galactose and mannitol — were also 

 observed but as these substances were all attacked with gas for- 

 mation they need not be considered. 



The investigations of Theobald Smith, Hardin, Rogers and 

 others indicate distinctly that the Voges-Proskauer positive or 

 methyl-red negative strains are so different from the Voges- 

 Proskauer negative, or methyl-red positive organisms with respect 

 to the end products of carbohydrate fermentation that subdivi- 

 sion upon these characters seems justified. Two groups are 

 therefore recognized, the methyl-red positive, Voges-Proskauer 

 negative or B. coll group and the methyl-red negative, Voges- 

 Proskauer positive or B. aerogenes-B . cloacae group. 



METHOD OF STUDY 



The organisms in each of the two groups are first tabulated as 

 in table 1 in order to facilitate the calculation of the correlation 

 coefficients which are then determined for each pair of characters 

 and recorded as indicated in table 1a. In choosing between any 

 two characters, that one which gives the highest coefficient of 

 correlation with the greatest number of other characters is selected 

 for subdivision. For the resulting subgroups new correlation 

 tables are prepared and subdivision again made as above. A 

 point is very quickly reached where further subdivision upon 



