Presumptive Tests for B. Coli. 151 



but according to American standards, Irons (Irons, 1902) 

 and Gage and Phelps (Gage and Phelps, 1903) conclude 

 that the group of organisms giving a positive neutral red 

 reaction is too large a one to give very valuable sanitary 

 information. 



Stokes (1904) urged the use of lactose broth with the 

 addition of neutral red, and believed that the production 



in this medium of 30-50 per cent of -gas with a — gas for- 



I 



mula and the change of neutral red to canary yellow in the 



closed arm of the fermentation was characteristic for B. 



coli. 



■ The lactose-bile method, however, is the only rapid 



test whose value has yet been established by a considerable 



series of investigations; it seems to be the best presumptive 



test now available. 



