248 



ALIPHATIC AND AROMATIC COMPOUNDS 



calcium and sodium salts of formic acid represents a simple case and may be shown 

 as follows: 



Ca(COOH).+H30 = CaC03+CO.+ 2H, , 



Na(COOH) +H.0=NaHC03+H, . 



The manner of decomposition of other organic acids has been studied in some in- 

 stances. A review of much of the older work is given by Harden.' More recently the 

 decomposition of citric acid has been studied by Brown, Duncan, and Henry, ^ and 

 fumaric, succinic, and pyruvic acids by Aubel' and Quastel.'' One example of the type 

 of breakdown accomplished by bacteria may be given, namely, the decomposition of 

 fumaric acid, an unsaturated dicarboxylic acid, by B. pyocyaneus.^ The main course 

 of fermentation is believed to proceed as follows with acetic acid and carbon dioxide 

 as the final products: 



COOH 



COOH 



CO +0 CH, 



I +C0. > +C0. 



CH, 



Pyruvic 



It has been suggested that the utilization of certain of the simpler aliphatic or 

 aromatic compounds might be used as a basis for the separation of different species 

 or groups of bacteria. A few of the more recent suggestions will serve to illustrate the 

 point. In a study of the alcaligenes group, Ayers, Rupp, and Johnson^ used organic 

 acid salts as test substances instead of the usual carbohydrates which in many in- 

 stances are not attacked by this group of bacteria. It has been further shown by Ayers 

 and Rupp7 that sodium hippurate is hydrolyzed to benzoic acid and glycocoU by 

 hemolytic streptococci of bovine origin but not by those of human origin. 



The availability of uric acid for certain members of the coli-aerogenes group has 

 been used to distinguish the coli from the aerogenes-cloacae subgroup.^ When given 

 this compound as the only source of nitrogen, B. aerogenes and its allies are able to 

 split the purine ring whereas B. coli lacks this ability. A somewhat similar distinction 

 has also been made, based on the utilization of citric acid by this group of organisms.'' 

 When this acid in the form of its sodium, potassium, or ammonium salt is supplied as 

 the sole source of carbon, fecal strains of B. coli are unable to develop. They apparent- 

 ly lack the ability to make use of the citrate radical while closely related types of soil 



' Harden, A.: Thorpe's Diclionary of Applied Chemistry, pp. 502-36. 191 2. 

 ' Brown, H. C, Duncan, J. T., and Henry, T. A.: loc. cil. 

 3 Aubel, E.: Bull. Soc. Chim. Biol., 6, 288. 1924. 

 ^Quastel, J. H.: Biochem. J., 18, 365. 1924; 19, 641. 1925. 

 5 Ibid. 



* Ayers, S. H., Rupp, P., and Johnson, VV. T.: loc. cit. 



7 Ayers, S. H., and Rupp, P.: ./. Infect. Dis., 30,388. 1922. 



* Koser, S. A.: ibid., 23,377. 191S. ' Koser, S. A.: ./. Bact., 8,493. 1923. 



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