METHODS FOR MICROSCOPIC STUDY OF BACTERIA 253 
not B. coli— give a positive reaction in glucose broth. The reaction 
seems to be elicited quite constantly in cultures of certain fermenting 
microbes which do not give a positive methyl red reaction^ (that is, 
cultures that give a low hydrogen-ion concentration, and a gas rate of 
CO2 _ 2-3n 
H2 l'\ 
Bacteria which ferment sugars grow^ in the closed arm of the fer- 
mentation tube; those organisms, with very few exceptions, which 
cannot utilize the carbohydrate of a fermentation medium fail to 
grow in the closed arm where free oxygen is not available; growth 
appears only in the open arm. 
Occasionally a very slight change in the stereo-isomeric formula 
of a carbohydrate, or a very small change in its terminal groups will 
determine its fermentability by various organisms. Thus glucose, 
mannose and their respective alcohols, sorbitol and raannitol, accord- 
ing to Emil Fischer,- have the following stereo-isomeric formulae:-^ 
H H 
I I 
H— C=0 H— C=0 H— C— OH H— C— OH 
I I I I 
H— C— OH HO— C— H H— C— OH HO— C— H 
I I I I 
HO— C— H HO— C— H HO— C— H HO— C— H 
I I I I 
H— C— OH H— C— OH H— C— OH H— C— OH 
I I I I 
H— C— OH H— C— OH H— C— OH H— C— OH 
I I I I 
H— C— H H— C— H H— C— H H— C— H 
I I I I 

H H H H 
D. Glucose. D. Mannose. D. Sorbitol. D. Mannitol. 
The fermentation of these hexoses and their respective alcohols 
by certain bacteria is shown in the accompanying table : 
Organism. 
D. Glucose. 
D. 
Mannose. 
D. 
Sorbitol. 
D. Mannitol. 
B. dysenterise Shiga . 
. . + 
+ 
- 
- 
B. dysenteriis Flexner 
. . + 
+ 
- 
+ 
B. Morgan No. 1 . . . 
. . + 
+ 
- 
— 
B. paratyphosus beta 
. . + 
+ 
+ 
+ 
B. proteus ..... 
. . + 
- 
- 
- 
Even more striking is the ability of certain strains of B. proteus 
and Vibrio cholerje to ferment glucose, but not mannose. The only 
difference between these hexoses is the arrangement of the H and OH 
groups around the carbon atom next to the aldehyde group. (See 
diagram above.) 
1 Rogers, Clark and Evans: Jour. Infec-. Dis., 1914, 15, 100; 1915, 17, 137. Perkins: 
Ibid., 1925, 37, 232. Paine: .lour. Bacteriol., 1927, 13, 269. 
- Untersuchungen iiber Kohlenhydrate und Fermente, 1884-1908, Berlin, 1902. 
' For convenience, the conventional straight chain formulae are used in place of the 
lactone formula. 
