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 



2 



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

 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. 



