1923] 



CAMP — CITRIC ACID AS A SOURCE OF CARBON 231 



is equipped to do careful work in organic chemistry. Currie 

 ('17) stated that citric acid might yield oxalic acid in the course 

 of metabolism, and my own work leads to the same conclusion, 

 nor is it surprising that a fungus which normally produces oxalic 

 acid from sugars should produce it from citric acid. 



There seems to be a general agreement among bacteriologists 

 that carbonates are formed by certain bacteria from the salts of 

 organic acids and that this accounts for the increasing alkalinity 

 of the solution. Maasen ('96) reported this finding for various 

 bacteria and even went so far as to show how the citric and other 

 acids were decomposed to form carbonates as end products. 

 Ayers and Rupp ('18), Wolf ('22), and others confirm these find- 

 ings. Wolf ( '22) explained the reversal of reaction of B. diphtheriae 

 cultures by the formation of alkali carbonates and gave figures 

 for the amounts of CO* obtained from cultures of various ages 

 as confirmatory proof. A critical examination of the data and the 

 reactions involved would seem to indicate that this explanation 

 might empirically delineate the situation, yet what actually 

 happens is that the carbonates are formed as a result of the in- 

 creasing alkalinity of the solution and as a consequence are a 

 result and not a cause. Cultures of fungi were shown to produce 

 an alkalinity as great as that produced by B. diphtheriae (see 

 Penicillium stoloniferum and P. sp.) without carbonates being 

 detectable in any appreciable amount. An inspection of the 

 various equilibria involved may explain the situation. 



H*CO» dissociates in two stages according to the following 

 two equations: 



+ 



(1) H,CO,!;H + +HC07 



(2) HCO, tZ H + + C07" 



Blasdale ('18) gives the dissociation constant (k) for the firsl 

 equation as 3 X 10~ 7 , and for the second equation as 3 X 10" 

 However, HiCOi is not stable in acid solution but decomposes t( 

 form HjO and CO». An alkaline carbonate, such as NajCO, 

 reacts according to the following equations when acid is added 



(3) Na,CO, + HC1 U NaCl + NaHCO, 



(4) NaHCO, + HC1 !~ NaCl + H s CO, 



(5) H,CO, 5 H,0 + CO, 



