86 UNIVERSITY OF WISCONSIN STUDIES 



dicate the nature of the fermentation which would take place 

 under certain very definite conditions. A variation in the 

 medium, even in the kind of pepton, may change the buffer 

 action so much that the test no longer serves the purpose for 

 which it was designed. For this reason, Clark and Lubs, 13 

 in a second paper, have proposed a synthetic medium which 

 will obviate this difficulty. 



Properly speaking the methyl red test cannot be considered 

 as a character correlated with the gas ratio. By indicating 

 the group to which the culture belongs, the necessity for de- 

 termining the gas ratio is obviated. The chemical changes 

 producing the reactions 011 which the test depends are the 

 changes which produce the distinct gas ratio and the two 

 are thus merely indicators of a fundamental difference in the 

 course of the fermentation. The methyl red test is so designed 

 that if it is properly manipulated it must be correlated with 

 the gas ratio. 



The Voges-Proskauer test. MacConkey and Clemesha 

 considered a positive Voges-Proskauer test as one of the 

 characters which distinguished B. aeroyencs from B. coli. This 

 view was confirmed by Levine, 14 and Johnson and Levine, 15 

 observed that there was a very high negative correlation be- 

 tween the methyl red test and the Yoges-Proskauer test. In 

 our own work we did not use the Voges-Proskauer test at first 

 but after the appearance of Levine 's paper, 374 cultures 

 which were then available were subjected to this test. The 

 results, which have been reported by Clark and Lubs, 10 show 

 a perfect correlation between the gas ratio, the methyl red 

 test and the Voges-Proskauer test. In some cases, however, 

 the reaction was so faint and disappeared so quickly that 

 without careful observation it would have been overlooked. 



The formation of acetyl-methyl-carbinol is not directly de- 



K; Loc. cit. 



14 Max. Levine, Preliminary Note on the Classification of Some Lactose 

 Fermenting Bacteria in Jour. Bact., 1, 6, pp. 619-621, 1916. 



15 B. R. Johnson and Max. Levine, Characteristics of Coli-like Microor- 

 (/anisms from the Soil in Jour. Bact., 2, 4, pp. 379-401, 1917. 



16 W. M. Clark and H. A. Lubs, Improved Chemical Methods for Differ- 

 entiating Bacteria of the Coli-Aerogenes Family in Journal Biol. Chem., 

 30, 2, pp. 209-234. 1917. 



