ELIMINATION OF SPURIOUS TESTS FOR B. COLI 347 



as capable of giving rise to a positive presumptive test in lactose 

 broth is important for these organisms are usually non-lactolytic. 

 Peculiarly these organisms grew, though slowly, upon the gentian 

 violet litmus lactose agar used for plating; their colonies could 

 easily be differentiated from the colon bacillus by the marked 

 manner in which they absorb the dye from the media. In 

 only 1 of the 3 was there a suggestion of acid reaction in the 

 plate and this was anything but marked. It suggests that 

 possibly these organisms produce gas through putrefaction, as 

 most of the anaerobic spore bearers are known to do in the 

 absence of fermentable carbohydrates. It also raises the ques- 

 tion as to whether some of the spurious presumptive tests which 

 bacteriologists have been in the habit of ascribing to anaerobic 

 spores may not be due to aerobic spores. This brings us to 

 another interesting point, namely that 16 of the gentian violet 

 litmus lactose agar plates made from these standard presump- 

 tive tests with heated water samples not only showed no acid, 

 but were absolutely barren for at least forty-eight hours. It 

 will be remembered that these plates in some of the other series 

 showed mainly, if not entirely, Gram-positive bacilli of the hay 

 bacillus group. The inhibition of this group in this last series 

 of tests is no doubt responsible for the fact that in the two 

 other instances plates showing acid colonies due to streptococci 

 were recorded. We recall that Krumwiede and Pratt (1914) 

 found streptococci and pneumococci somewhat more resistant 

 to gentian violet than some other Gram-positive bacteria. 



None of these heated samples however gave positive presump- 

 tive tests in the lactose broth with gentian violet. The four 

 positives obtained were from samples of which plates from the 

 standard test were sterile, as mentioned. In one case the fer- 

 mentation tube was full of gas in twenty-lour hours; B. coli was 

 isolated from among the acid colonies on the plate. In one 

 other an aerobic, acid forming spore was found to comprise the 

 single colony on the plate. The presumptive test in this in- 

 stance though showing no gas till the fourth day then developed 

 a tube full, at the same time showing a marked decolorization 

 of the dye. The 2 other positive presumptives showed gas only 



