26 BULLETIN 782, U. S. DEPARTMENT OF AGRICULTURE. 



The results of the study of the fermentation of the organic-acid 

 salts indicate that some of the bacteria could obtain their carbon 

 from the methyl, alcohol, or aldehyd (as in formic acid) radical of 

 the salts of organic acids but not from the carboxyl group. Carbon 

 was most easily obtained from the methyl group, as is shown from 

 Table 11, where it is seen that most of the cultures were able to obtain 

 their carbon from acids which had no alcohol radical, such as succinic 

 or acetic. They were able to obtain it to about the same extent 

 from citric, malic, and lactic acids, which contained both the methyl 

 and alcohol radicals. In this case it is believed that the methyl 

 radical supplies the carbon, since acids containing merely the alcohol 

 radicals were not readily fermented. Only a small number of the 

 cultures utilized the carbon from- the alcohol radical where it was 

 Unked with a carboxyl and another alcohol radical, as in mucic, 

 tartaric, and glyceric acid. The carbon did not seem to be utilized 

 from an alcohol radical linked only to a carboxyl radical, as in 

 glycolic acid. Pyruvic acid was easily fermented by all the cultures, 

 and in this case the carbon may come from either the methyl or 

 ketone radical. A, Fischer mentions in his book " The Structure and 

 Functions of Bacteria," published in 1897, that bacteria are able 

 to utilize carbon from the methyl radical more readily than from the 

 alcohol radicals and they are unable to utilize the carbon from the 

 carboxyl radical^ as in oxalic acid. Our results confirm his opinion 

 in the matter. 



When the salts of organic acids were fermented an alkaline reaction 

 was produced in most cases, the exceptions being butyric, valeric, 

 and caproic acids. In the case of these acids the fermentation may 

 proceed in one of two ways: Either the methyl radicals may be 

 oxidized imtil a carbonate is produced and the medium becomes 

 alkaline, or the acid may be split into other acids containing fewer 

 carbon atoms. For example butyric may be oxidized as foUows: 



CH3 CH2 CH2 COOH+02=2 CH3 COOH 



butyric acetic 



CH3 CH2 CH2 COOH+02=HCOOn+CIl3 CH, COOH 

 butyric formic propionic 



The oxidation of butyric acid to other acids may account for the 

 increased hydrogen-ion concentration produced by certain alkali 

 bacteria, since under ordinary conditions this concentration is lowered 

 by the production of carbonates. Both these forms of fermentation 

 may take place at the same time, but in the great majority of cases 

 one or the other predominated, as is shown in Table 10. While 

 many of the cultures produced an acid reaction in n-butyric and 

 n-valeric acids, all those which fermented isobutyric, a or fi oxy- 

 butyric, and isovaleric acids produced an alkaline reaction. 



