20 
BULLETIN 782, U. S. DEPARTMENT OF AGRICULTURE. 
acid salts might be utilized as a source of carbon and thereby become 
valuable substances for fermentation tests. 
In 1895 Maassen (7) studied the fermentation of 21 different or- 
ganic-acid salts by 52 varieties of bacteria, He obtained some growth 
with all these cultures in media containing the various organic-acid 
salts. As Maassen used these salts in a medium containing pep- 
tone, it is not surprising that he obtained positive results with all 
the organic acids, for the reason that the carbon could probably have 
been obtained by the bacteria from either the organic acid or the 
peptone, according to which one was the more available. If these 
organic-acid salts are to serve as carbon-containing test substances 
they must be used in a medium containing no other source of carbon. 
In order to determine the value of the salts of the organic acids as 
a source of carbon, the fermentation of 24 of these salts by the alkali- 
forming group of bacteria was studied. The fermentation was deter- 
mined in a synthetic medium of the following composition: 
XaXH 4 HPO gram. . 0. 50 
XaH 2 P0 4 .do 17 
KC1 do 20 
Water, distilled c. c . . 1, 000 
Acid (neutralized with XaOH) grams. . 1.2 
Urea and hippuric and uric acids were also used in the following 
media: 
L'rea grams.. 
2.00 
Hippuric acid . gram . 
1.0 
Uric acid gram. . 
1.0 
Xa 2 HP0 4 ....gram.. 
.50 
XaOH quantity suf- 
XaOH grams. . 
8.00 
KC1 do.... 
.10 
ficient to neutral- 
KC1 gram. . 
.10 
NaH 2 P0 4 do.... 
.17 
ize the acid. gram. 
.50 
Water.distilled.ee. 
1,000 
Water, distilled, c.c. 
1,000 
XaH 2 P0 4 do.. 
.17 
Filter through Berke- 
KC1 do.. 
.10 
feld). 
Water c. c. . 
1,000 
It is evident from the composition of the medium that if growth 
occurs the carbon must be obtained from an organic-acid salt. The 
fermentation of the organic-acid salts was measured by the change 
in the hydrogen-ion concentration. A change of more than P H 0.2 
being recorded as a positive fermentation. An exception is taken 
in recording the results of the fermentation of butyric, valeric, and 
caproic acids where any change from the control is recorded as posi- 
tive because of the possibility that these acids were split into simpler 
acids, and these simpler acids in turn oxidized to alkaline carbonates. 
The final hydrogen-ion concentration of the medium would in such 
cases depend upon the point in the fermentation at which it was 
determined. In every case a change in hydrogen-ion concentration 
from the control showed growth in the tubes. The complete result 
of the study is given in Table 10. It will be seen in the tabulated 
