244 ALIPHATIC AND AROMATIC COMPOUNDS. 



Investigations along this line have been many and varied, and the results at times 

 have been contradictory.' In spite of this, however, certain general conclusions may be 

 drawn. A number of the commoner saprophytic types, B. fluorescens, B. pyocyancus, 

 B. prodigiosus, B. proteus, B. coli, and probably others, are able to satisfy their ni- 

 trogen and carbon requirements when a single mono-amino acid such as alanine is 

 added to a solution of certain inorganic salts, though the development under such 

 conditions will not be as rapid or luxuriant as in nutrient broth. If a readily available 

 source of carbon such as lactic acid, glycerol, or dextrose is also supplied, the value of 

 the medium is enhanced and certain organisms which experienced difficulty in appro- 

 priating the amino acid for their own uses will speedily break down these more readily 

 available sources of carbon and energy, and at the same time derive their nitrogen 

 from the amino acid. A surprising number of organisms are able to develop under 

 such conditions. Among the better-known forms are the green fluorescent bacilli, B. 

 pyocyaneus, B. prodigiosus, B. proteus, the coli-aerogenes group, certain members of 

 the paratyphoid group, and a few spirilla. The tubercle bacillus and other acid fast 

 types are also able to satisfy their nutritive requirements from very simple sources 

 of nitrogen and carbon.^ Most of the pathogens, however, are unable to develop 

 under these conditions, and negative results have usually been reported for the ty- 

 phoid and dysentery bacilli, B. abortus, B. diplitheriae, the pneumococcus, streptococci, 

 and staphylococci of various types, to mention only some of the commoner ones. 



The question of the relative values of the various amino acids may be regarded as 

 still an open one, for there is much conflicting evidence. In many instances an or- 

 ganism, if able to satisfy its nitrogen requirements from one of the mono-amino acids, 

 may be expected to make use of the others, although exceptions to this have been re- 

 ported. Lysine, arginine, histidine, and tryptophane are other amino acids which offer 

 additional nitrogenous groupings. It has been claimed that they possess an added 

 nutritive value in some instances while in others they appear to be of no more value 

 than the simpler mono-amino acids. Dipeptides, also, are susceptible to bacterial 

 attack^. Glycyl-glycine, glycyl-tyrosine, glycyl-tryptophane, and other combina- 

 tions are split by a number of organisms, and the separate amino acids may be re- 

 covered if they are not in turn utilized. Finally, in considering the utilization of amino 

 acids or related compounds it should not be overlooked that at least certain of them 

 have been found to exert a toxic or inhibitory effect upon the growth of some of the 

 more "fastidious" bacteria.^ 



The mode of attack and the steps in the breakdown of the amino acids present an 

 interesting though a complex problem, for we may have both nitrogen and carbon 



' For reviews of earlier work and bibliography see Gordon, M. H.: J . Roy. Army M. Corps, 28, 

 371. 1917; Koser, S. A., and Rettger, L. F.: J. Infect. Dis., 24, 301. 1919; Braun, H., and Cahn- 

 Bronner, C. E.: Cenlralbl.f. Baklcriol., Abt. I, Orig., 86, 196 and 380. 1921; Krasnow, F.,Rivkin, H., 

 and Rosenberg, M. L.: /. Bad., 12, 385. 1926; den Dooren de Jong, L. E.: Bijdragc tot de kennis van 

 lift mineralisaticproccs, pp. 1-200. Rotterdam: Nijgh and Van t)itmar, 1926. 



^ Long, E. R.: Am. Rev. Tiibcrc, 3, 86. 1919; 5, 857. 1922. 



3 Sasaki, T.: Biochem. Zlsclir., 41, 174; 47, 463 and 472. 1912; Otsuka, I.: Physiol. Ahst., 2, 

 15. 1917, 



■• Gordon, J., and MrLeod, J. W.: ./. Path. & Bail., 29, 13. 1926. 



