20 



BULLETIN 782, U. S. DEPAKTMENT OF AGKICULTUEE. 



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 siu-prising 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 : 



NaNH4H.P0 gram.. 0.50 



NaH2P04 do 17 



KCl do 20 



Water, distilled c. c. . 1, 000 



Acid (neutralized with NaOH) grams. . 1. 2 



Urea and hippuric and uric acids were also used in the following 

 media : 



Urea grams.. 



2.00 



Hippuric acid . gram . 



1.0 



Uric acid gram.. 



1.0 



Na2HP04 gram.. 



.50 



NaOH quantity suf- 





NaOH grams.. 



8.00 



KCl do.... 



.10 



ficient to neutral- 





KCl gram . . 



.10 



NaH2P04....do...- 



.17 



ize the acid .gram . 



.50 



Water, distilled. c.c. 



1,000 



Water, distilled. c. c. . 



1,000 



NaH2P04 do.. 



.17 







Filter through Berke- 





KCl 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 Pg 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-ioh 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 



