276 MAX LEVINE 



only with respect to motility, and it may therefore be well to 

 regard it as a variety of B. communior. However B. coscoroba 

 is so distinctly different from the other sucrose fermenters that its 

 designation as a species seems justified. It should be borne in 

 mind however, that the differentiation in this instance is based 

 on only 9 individual cultures so that the correlations observed 

 must not be over emphasized. 



CONCLUSIONS 



To treat all characters as of equal taxonomic significance leads 

 to an infinite number of unstable varieties; a condition to be 

 avoided. 



Subdivision on correlated characters results in a small number 

 of groups which possess considerable stability. 



The species described are quite strikingly correlated with the 

 source, and, if more extensive investigations confirm these ob- 

 servations, recognition of the various species may be of sanitary 

 significance. 



It is not supposed that the classification presented is the last 

 word in the differentiation of coli-like bacteria, but it is hoped 

 that if subdivision is to be made upon correlated characters — and 

 there is much to commend such a procedure — the method de- 

 scribed in this paper for the determination of the best correlated 

 character, by a study of the coefficients of correlation, will be an 

 aid to later investigators. 



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Durham, H. E. 1901 J. Exper., 5, 353. 



Ford, W. W. 1903 Studies from the Rockefeller Inst, of Med. Res. 11. 



Howe, E. C. 1912 Science, N. S., 35, 225. 



Jackson, D. D. 1911 Am. J. Pub. Health, 1, 930. 



Johnson and Levine 1917 J. Bact. 



Kligler, I. J*., 1914 J. Infect. Dis., 15, 135. 



Levine, M. 1916 J. Infect. Dis., 19, 773. 



MacConkey, a. 1905 J. Hyg. 5, 333; 1909 J. Hyg. 9. 



Rogers, et al. J. Infect. Dis., 1914, 14, 411; 1914, 15, 100; 1915,[l7,^137. 



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