ALKALI-rOKMING BACTERIA FOU^STD IN MILK. 21 



results in the table that nearly aU 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 alkah-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 

 (CH3COCOOH) comprises a ketone (CO) radical connecting a methyl 

 (CH3) 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 

 CH3 



lactic acid, CHOH. The cultures were able to obtaia 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. 



