54 MARGAEET C. PEBRY AND W. F. MONFORT 



The strains described by Johnson and Levine (1917) from soil 

 include four methyl red neutral, Voges-Proskauer positive; 

 13 methyl red neutral, Voges-Proskauer negative; and 2 methyl 

 red negative, Voges-Proskauer negative. The temperature and 

 period of incubation differ from those now current, but con- 

 cordant results recorded in the same paper are cited by Rogers, 

 Clark and Lubs (1918) and by Winslow, KUgler and Rothberg 

 (1919). 



Burton and Rettger (1917) report the biometric method 

 inappUcable to the colon-aerogenes group on account of the 

 marked variability of organisms of the high ratio type with 

 respect to the methyl red test in Clark and Lubs medium (1915) 

 as well as in others employed. While variability with regard to 

 the Voges-Proskauer reaction was noticeable, it was less frequent 

 than in the methyl red test. They refer to two cases found by 

 Rogers, Clark and Davis (1914) and Rogers, Clark and Evans 

 (1915) where an organism had apparently altered its gas ratio 

 profoundly, explained by the authors as possibly due to an error 

 in lettering apparatus, remarking that this is undoubtedly the 

 safer explanation, but that in view of the results of themselves 

 and others in this field variability must also be reckoned with. 

 In explaining variability of high ratio organisms they suggest 

 that metabolism may take two courses, not necessarily parallel 

 or of equal rate : the fermentations may proceed irregularly and 

 yield equivocal results even when the Witte peptone broth of 

 Clark and Lubs is used. With the same strain there may be 

 rapid exhaustion of sugar, heavy growth, large gas volume, 

 high gas ratio and low acidity; or incomplete sugar utilization, 

 small gas volume, low gas ratio, and high acidity. If neither 

 factor predominates it would be possible to have an organism 

 capable of giving the Voges-Proskauer reaction and an acid 

 reaction with methyl red. The authors cite one strain which 

 became persistently methyl red positive and Voges-Proskauer 

 positive. 



Burton (1916) in his thesis, of which Burton and Rettger pre- 

 sent the summary, instances 50 strains from sources, mostly 

 unpolluted, which gave conflicting or variable methyl red and 

 Voges-Proskauer reactions. 



