68 ELEMENTS OF WATER BACTERIOLOGY. 



differing from the type in one or two of its character- 

 istics. 

 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 C0 2 , is quite abnormal. But in spite of all these 

 facts, the bacillus tested may have been originally a true 

 Bacillus coli." 



The more of such atypical forms which are included 

 the greater will be the number of positive isolations. At 

 present our definitions must be more or less arbitrary; 

 each observer will consider as true colon bacilli those 

 which fulfil his particular set of tests, and will class as 

 pseudo-colon organisms those which do not. If we find, 

 having established such an arbitrary standard, that the 

 colon bacillus, as determined by it, is found in waters 

 known to be polluted, and not, as a rule, in those known 

 to be free from pollution, the sanitarian can afford to 

 ignore the theoretical question of specific values and 



