12 BULLETIN 782, U. S. DEPARTMENT OF AGRICULTURE. 
FERMENTATION OF CARBOHYDRATES. 
DEXTROSE. 
In some previous work with a small number of cultures of alkali- 
forming bacteria, it was found by Ayers and Johnson (2) that while 
they apparently did not ferment sugars, an alkaline reaction was 
usually produced. In recent work, however, with a larger number 
of cultures it has been found that certain carbohydrates were 
fermented but that special means have to be taken to determine 
this action. 
Extract broth is not always a suitable medium in which to deter- 
mine the fermentation of dextrose, as is shown by the results in Table 
4. The broth had the following composition: Dextrose 1.0 per cent, 
beef extract 0.4 per cent, peptone 1.0 per cent, and distilled water. 
The reaction was brought to the neutral point, the solution filtered, 
the dextrose added, and the medium sterilized. The final reaction 
was about plus 0.2 (Fuller's scale). The cultures were incubated 
at 30° C. for 7 days and a duplicate set for 21 days, and titrated 
at the end of each incubation period. The figures in the table repre- 
sent the change in titration from the control, 10 cubic centimeters 
of medium being titrated with tenth-normal sodium hydrate. The 
fermentation was considered positive when 1 per cent or more normal 
acid was formed, since this is the usual amount considered to indicate 
fermentation. An examination of the results shows that after 7 
days' incubation 15 of the cultures showed an acid fermentation in 
dextrose and 10 showed such a reaction after 21 days. With 13 of 
the cultures a higher acidity was found after 7 days than after 21 
days, while 7 showed more acid after the longer incubation. After 
7 days' incubation 3 of the cultures were acid but after 21 days were 
alkaline, while 3 other cultures were alkaline after 7 days and became 
acid after 21 days. It will be noted in Table 4 that 3 cultures 
produced gas from dextrose. These results show that the fermenta- 
tion of dextrose by the alkali-forming group of organisms was very 
indefinite when determined in the ordinary manner by titration in 
the regular broth medium. Some cultures showed a distinct and 
others only a slight fermentation, while many produced only an 
alkaline reaction. 
As previously noted, it was found that these bacteria produced 
alkaline reaction when grown in beef -ex tract broth without sugar. 
The broth contained 0.2 per cent beef extract and 0.5 per cent 
sodium-dibasic phosphate. While this is not exactly the same 
composition as that of the dextrose-extract broth, the results of 
titrations help to explain some of the peculiar results obtained in 
the dextrose fermentation, and they are incorporated in Table 4. 
It may be seen that all the cultures of this group gave an alkaline 
change in titration after 14 days' incubation in beef-extract broth; 
