Other Intestinal Bacteria. 155 



of polluted waters. On the other hand, in the study of 

 259 samples of presumably unpolluted waters, by the 

 method of direct plating, Nibecker and one of the authors 

 (Winslow and Nibecker, 1903) found streptococci in only 

 one sample. Gordon (1904) showed that certain strep- 

 tococci are abundant in normal saliva and are found 

 in air which has been exposed to human pollution but not 

 in normal air. On the whole there can be no doubt of 

 the fact that streptococci occur on the surfaces of the 

 human and animal body more commonly than anywhere 

 else in nature. 



The isolation of these organisms either from plates or 

 liquid cultures is easy. On the lactose-agar plate!, made 

 directly from a poUiited water, the colonies of the strep- 

 tococci may generally be distinguished from those of other 

 acid-formers by their small size, compact structure, and 

 deep-red color, which is permanent, never changing to 

 blue at a later period of incubation. Developing some- 

 what slowly, however, they may be overlooked if present 

 only in small numbers. In the dextrose-broth tube, strep- 

 tococci will generally appear in abundance after a suit- 

 able period of incubation. Prescott and Baker, in the 

 work above mentioned, found that with mixtures of B. 

 coli and streptococci in which the initial ratios of the 

 latter to the former varied from i: 94 to 208: i, the colon 

 bacilli developed rapidly during the early part of the 

 experiment, reaching a maximum after about fourteen 

 hours, and then diminishing rapidly. The streptococci 



