Isolation of the Colon Bacillus. 101 



mycoides) are present, a dull wrinkled growth will be 

 produced. 



Having submitted the sample of suspected water to a 

 preliminary enrichment process, and having isolated pure 

 cultures of suspicious organisms from the litmus-lactose- 

 agar plate, the third step is the examination of the specific 

 reactions of the organisms thus obtained. Just what 

 characters to use in denning the "colon bacillus" is a 

 matter of prime importance. The whole question of 

 species among the bacteria is an extremely complex one, 

 since around each definite species are grouped forms 

 differing from the type in one or two of its characteristics. 



As Whipple says (Whipple, 1903), "The type form of 

 Bacillus coli is one which can be defined within reason- 

 ably narrow limits, but when the organism has been away 

 from its natural habitat for varying periods of time, and 

 has existed under abnormal conditions, its ability to react 

 normally to the usual tests appears to be greatly impaired. 

 Its power to reduce nitrates may be lost, or on the other 

 hand may be increased; its power to produce indol may 

 be lost, or on the other hand it may be increased; its 

 power to coagulate milk, even, is sometimes reduced, 

 although seldom entirely lost; its power to ferment car- 

 bohydrates may be altered so that the amount of gas 

 obtained in a fermentation tube, as well as its ratio of 

 H to CO 2, is quite abnormal. But in spite of all these 

 facts, the bacillus tested may have been originally a true 

 Bacillus coli." 



