S. A. KOSER 247 



the fatty-acid series and a few of their hydroxy derivatives, some members of the 

 dicarboxyUc and tricarboxyHc series, and aromatic acids containing the phenyl radical. 

 The outline will serve to show the wide variety of chemical groupings which are pre- 

 sented. 



In the presence of a suitable source of nitrogen many of these acids or their salts 

 are broken down and utilized, though a few appear to be relatively resistant to bac- 

 terial attack. Benzoic and salicylic acids, in which the carbon is contained in the car- 

 boxyl group and the benzene ring, appear to present a formidable obstacle to most 

 organisms, and very few types are able to make use of them. Oxalic acid with two 

 carboxyl groups joined directly is also resistant to most bacteria. Whether this is due 

 to an inability of the organism to make use of this type of structure or whether it is 

 due to the poisonous character of the compound is not clear. When the two carboxyls 

 are linked by a methyl group, as in malonic acid, the compound is attacked by certain 

 organisms which are unable to make use of oxalic acid, for example, some members 

 of the alcaligenes group and the coli-aerogenes group. Succinic acid appears to lend 

 itself still more readily to bacterial attack, surprising as this may seem, for it is rela- 

 tively resistant to chemical oxidizing agents. Many of the other acids are readily 

 utilized by the commoner saprophytic bacteria and molds, and in some cases by 

 pathogenic types.' Lactic acid, for example, when supplied as the only source of car- 

 bon and with a suitable inorganic nitrogen compound will support development of the 

 coli-aerogenes group, the alcaligenes group, the green fluorescent bacilli, and even cer- 

 tain members of the paratyphoid group. 



A comparison of the structural formulas of these acids with their utiHzation by 

 various types or groups of organisms presents an interesting field though it is impossi- 

 ble to review the results at length here. Suffice it to say that a slight change in the 

 structure of a compound or even the presentation of a different isomer may alter 

 materially its availability for certain organisms though perhaps not for others. 

 Furthermore, we are not always able to predict the utilization of a compound by 

 micro-organisms from a consideration of their behavior toward a similar chemical 

 grouping in another compound. 



As might be expected, the utilization of organic acid salts is influenced markedly 

 by the oxygen supply. Under aerobic conditions many bacteria will develop in a much 

 simpler medium than they require for anaerobic life. Coliform organisms can develop 

 in a simple inorganic salt medium with ammonium lactate under aerobic conditions, 

 while under anaerobic conditions other substances such as a fermentable sugar are 

 required. Supposedly, the sugar is required for anaerobic growth because it can be 

 disintegrated without the intervention of oxygen in such a way as to supply energy, 

 whfle this is not possible with salts of lactic acid.^ 



In the breakdown of the organic acids akaline end-products are frequently 

 formed. These are usually carbonates and bicarbonates. The decomposition of the 



■ den Dooren de Jong, L. E.: loc. cil.; Avers, S. H., Rupp, P., and Johnson, W. T.: U.S. Depl. 

 Agr., Bull. 782. IQ19; Koser, S. A.: J. Bad., 8, 493. 1923; Brown, H. C, Duncan, J. T., and Henry, 

 T. A.: J. Hyg., 23, i. 1924. 



^ Braun, H., and Cahn-Bronner, C. E. : loc. cit.; Stephenson, M., and Whetham, M. D. : Biochcm. 

 J ., 18, 498. 1924; Quastel, J. H., and Stephenson, M.: ibid., 19, 660. 1925. 



