190 ELEMENTS OF WATER BACTERIOLOGY 

 PRIMARY SUBDIVISIONS OF THE COLON GROUP 



The fourth group, fermenting saccharose, but not 

 dulcite, was further subdivided by MacConkey into 

 the B. coscoroba type, which does not liquefy gela- 

 tin or give the Voges and Proskauer reaction, the B. 

 lactis-aerogenes type, which does not liquefy gelatin, 

 but does give the Voges and Proskauer reaction, and the 

 B. cloacae type, which liquefies gelatin and gives the 

 Voges and Proskauer reaction. Records of the preva- 

 lence of the four principal groups in human and animal 

 faeces and in milk are given in MacConkey's two papers 

 (1905 and 1909) as well as their relative numbers in a 

 suspension of faeces in water after various intervals of 

 time. The results do not, however, appear to us to 

 justify any important practical conclusions. 



In his later paper MacConkey (1909) carried the 

 sub-division of the colon group much further. He 

 isolated 497 lactose-fermenting bacilli from the faeces 

 of man and animals, from sewage, water, grains, etc. 

 All were Gram-negative, fermented lactose, coagulated 

 milk and reduced nitrate. They were subdivided 

 by their action on gelatin, pepton and various fer- 

 mentable substances and by their motility into over 

 100 types of which the more important have received 



