344 



IVAN C. HALL AND LILLIAN J. ELLEFSON 



Since 5 samples, unheated and tested in gentian violet lac- 

 tose broth failed to produce gas in five days, we conclude that 

 B. coll, present as shown by previous tests, had disappeared 

 from the sample. All 5 showed gas in the presumptive test 

 without gentian violet — interpreted in all but one, from which 

 B. coli was isolated with some difficulty — as due to anaerobes. 



In addition to the last tests, examinations were made of 22 

 fresh samples, according to the same technic. The data of 

 table 4 are comparable, therefore, to those of table 3 except 

 that the samples had not stood so long. 



TABLE 4 



Tests for B. coli and sporiilating gas-forming anaerobes in 22 samples of icater- 

 using 1-20,000 gentian violet in the presumptive test 



* Same sample — "attenuated" B. coli fermenting lactose anaerobically but 

 not aerobically. 



t Same sample — B. coli not killed by heating. 



Analysis of the data shows that this series of samples pos- 

 sessed anaerobic sporulating gas formers in at least 19, or 95 

 per cent, of the samples according to the standard presumptive 

 test in lactose broth with the heated specimens. In the odd case 

 B. coli which had escaped the heating was isolated; its occurrence 

 in the standard test, and not in the dye test of the heated sample, 

 must have been fortuitous since the organisms could be shown 

 not to be inhibited by gentian violet. There were no positive 

 presumptive tests with the heated sarhple having gentian violet. 

 Of the positives in the standard test 12 were tested on a lactose 

 agar plate containing 1-10,000 gentian violet; in only one case 

 did growth appear, which consisted of a mixture of thick Gram 



