Nitrogen Metabolism of Bacteria 5 



in the course of metabolism, and in the kinds of chemical products which they 

 yield by means of such alteration. Two factors must always be considered in 

 studying the chemical products of bacterial action ; namely, the species of the 

 organism and the nature of the substance being acted upon. Upon the same 

 substrate different species may yield very different products ; likewise, as would 

 be expected from a unicellular organism, the same species may yield quite dif- 

 ferent products when grown on media of different chemical compositions. The 

 actual chemical processes involved in the decomposition of nitrogenous com- 

 pounds by bacteria are difficult to study. Equations which have been written 

 to represent such decompositions must, for the most part, be placed in the class 

 of speculations. Such speculations are of great value, however, and, no doubt, 

 frequently arrive very close to the truth. 



That proteolysis through the agency of bacteria capable of attacking native 

 proteins pursues the same general course as that brought about by the digestive 

 enzymes of the alimentary tract of animals seems to have been established 

 beyond dispute. Emmerling and Rieser° showed that B. fluorescens-liquefaciens 

 digested gelatin with the formation of proteoses and peptones. These were 

 later broken down to lower compounds yielding in the course of a month 25% 

 of their nitrogen in the form of ammonia. Substitution compounds of ammonia 

 were also found in the form of methylamin, trimethylamin, betain, and cholin. 

 That amino-acids were an intermediary product, however, was evidenced by 

 the fact that they were able to identify arginin and leucin. Cultures of the 

 same organism on fibrin solutions contained tyrosin, leucin, arginin, and 

 aspartic acid. Emmerling" identified the amino-acids, tyrosin and leucin, in 

 cultures of virulent streptococci on blood fibrin. Mono- and trimethylamins 

 were present here also, as well as pyridin bases. According to Taylor,' B. coli 

 digests pure casein mainly to proteoses and peptones, no appreciable quantities 

 of animo-acid being formed. On the egg-meat mixture employed by Rettger' 

 this organism produced profound changes, giving rise to the aromatic com- 

 pounds indol and skatol, the amino-acids tyrosin, leucin, and tryptophan being 

 identified as intermediary products. Proteoses and peptones were formed also. 



In the decomposition of proteins the obligate anaerobes play a most impor- 

 tant part. In fact, according to Rettger," true putrefactive changes with the 

 production of the foul-smelling mercaptans and hydrogen sulfid are brought 

 about only by this class of organisms, the part played by the aerobes and 

 facultative anaerobes being that of creating an oxygen-free environment and 

 removing the waste products of the strict anaerobes. From his researches it 

 appears that B. putrificus, B. oedematis, and the bacillus of symptomatic anthrax 

 are the most powerful putrefying organisms among the commoner anaerobes. 

 B. tetanus and B. welchii have little or no putrefactive power, the latter being 

 primarily a fermenting organism. 



The decomposition of the primary products of protein hydrolysis by bacteria 

 has been studied but little, altho mixtures of peptones and proteoses sold as 

 peptone have long been the favorite basic substance in bacterial culture media. 

 By means of the change in the rotation of polarized light, Abderhalden. 

 Pincussohn, and Walther" studied a number of the common pathogens with 



■■■ Ber. d. deutsch. chem. Gesellsch., 1902, 35, p. 702. 

 " Ibid., 1897, 30, p. 1863. 

 ' Ztschr. f. physiol. Chem., 1902, 36, p. 487. 

 s Am. Jour. Physiol., 1903, 8, p. 284. 



» Rettger and Newall: Jour. Biol. Chem., 1912, 13, p. 341. Rettger: Ibid., 1906, 2, p. 71; 

 1908, 4, p. 45. 



'0 Ztschr. f. physiol. Chem., 1910, 68, p. 471. 



