340 



IVAN C. HALL AND LILLIAN J. ELLEFSON 



the slightest growth upon such a plate. The same organism 

 was isolated from the presumptive test without gentian violet, 

 and we believe its presence in the unheated sample was the 

 reason for our failure to secure B. coli from this sample, from the 

 presumptive test either with or without gentian violet although 

 on the occasion of two other independent tests B. coli was iso- 

 lated from the same sample. At least 16, or 76 per cent, of the 

 21 samples contained gas-forming anaerobes, as shown by posi- 

 tive presumptive tests in plain lactose broth with the heated 

 samples from which only non-lactolytic aerobes appeared on the 

 litmus-lactose-agar plate subcultures; these were stained by 



TABLE 2 



Tests for B. coli and sporiilating gas-forminQ anaerobes in 21 samples of water — 

 using 1-100000 gentian violet in the presumptive test 



* Gas in presumptive tests and acid on plates due to laotolytio aerobic spore 

 bearers. 



Gram's method and were found to be Gram-positive sporulating 

 bacilli with one exception which contained Gram-positive cocci. 

 Two heated samples also giving positive presumptive tests in 

 plain lactose broth yielded acid colonies on litmus lactose agar; 

 the organisms were lactolytic aerobic spores. Anaerobic spores 

 may also have been present but we cannot be sure, and the per- 

 centage of samples certainly having anaerobic spores is given 

 exclusive of these two. 



As table 2 shows, all the samples showed gas in the plain 

 lactose broth tube inoculated with 10 cc. unheated water, as 

 against only 20 in the gentian violet lactose broth. But of the 

 20 there were 14 which produced acid colonies on litmus-lactose- 



