86 UNIVERSITY OF WISCONSIN STUDIUS 
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,¥ 
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 on which the test depends are the 
changes which produce the distinet 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. aerogenes from B. coli. This 
view was confirmed by Levine,* and Johnson and Levine,” 
observed that there was a very high negative correlation be- 
tween the methyl red test and the Voges-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,’® show 
a perfeet 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-anethyl-earbinol is not directly de- 
+ Loe. Cit, 
“Max, Levine, Preliminary Note on the Classification of Some Lactose 
Iermenting Bacteria in Jour, Bact., 1, 6, pp. 619-621, 1916. 
“B. R. Johnson and Max. Levine, Characteristics of Coli-like Microor- 
yanisms from the Soil in Jour, Bact., 2, 4, pp. 379-401, 1917. 
“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. 209-224, 1917. 
