ALKALI-FORMING BACTERIA FOUND IN MILK. 21 
results in the table that nearly all the organic-acid salts used were 
fermented to a greater or less extent. In the table are the results 
of hippuric and uric acids and urea, these substances being included 
merely for the sake of convenience; their fermentations will be dis- 
cussed later. 
Before proceeding with the fermentation of the salts of the organic 
acids it is necessary to call attention to the fact that the growth in 
the synthetic medium as used in this investigation with the organic- 
acid salts as a source of carbon was usually quite different in appear- 
ance from the growth obtained in the sugar broths. It was found 
that the alkali-forming bacteria frequently grew in a mass in the 
bottom of the tube and left the medium perfectly clear. Often when 
the greatest change in the hydrogen-ion concentration was noticed 
there was little appearance of growth in the tubes; at other times 
the medium became extremely cloudy. 
In connection with the fermentation of these organic-acid salts 
an attempt has been made to determine from which radical or 
radicals the carbon was obtained. The organic acids are grouped, 
therefore, in Table 11 according to the radicals they contain. For 
example citric, malic, and lactic acids are grouped together for dis- 
cussion because they contain a secondary or tertiary alcohol radical 
linked to a carboxyl and to a methyl radical. 
It will be seen in Table 11 that all the 68 cultures studied were 
able to utilize carbon from the sodium salt of pyruvic acid. The 
table gives the structural formula of the different acids but it must be 
remembered that the sodium salt was employed. Pyruvic acid 
(CHgCOCOOH) comprises a ketone (CO) radical connecting a methyl 
(CH 3 ) and carboxyl (COOH). It seems that carbon was readily 
available from an acid of this structure. This acid was sterilized 
by passage through a Berkefeld filter so as to prevent decomposition 
by heat. The cultures also obtained their carbon readily from other 
oxyacids, such as citric, malic, and lactic. In such acids an alcohol 
radical connects the carboxyl to the methyl group, as illustrated by 
CH S 
I 
lactic acid, CHOH. The cultures were able to obtain their carbon 
I 
COOH 
almost as well from salts of such acids as succinic, acetic, propionic, 
butyric, valeric, and caproic, in which there is no alcohol radical, 
but one methyl group is linked to a carboxyl. 
