LEO F. RETTGER 219 



pyocyanea, 9.79; C. diphtheriae, 9.55. These are not very unlike the results obtained 

 by Vaughan and Wheeler. 



Quite recently Seibert' isolated from tuberculin a nitrogenous substance in crys- 

 talline form which possesses the properties of ordinary protein and which appears to 

 embody the active principle of tuberculin, ^ 



The struggle for existence of bacteria means a struggle to furnish for themselves 

 the energy and cell substance necessary to multiply and to reproduce their own kind. 

 Organic carbon is, as a rule, the source of energy, and is supplied in various forms, as, 

 for example, carbohydrates, organic acids, alcohols, CO, CO2, and CH^. The carbon 

 of amino acids and acid amides also serves the same purpose. Carbon is necessary also 

 to build up organic cell structure, as are nitrogen, hydrogen, oxygen, phosphorus, 

 and sulphur. 



The exact nature and composition of proteins generally is still a matter of con- 

 jecture. The quantitative determination of the chemical elements in various known 

 proteins has revealed some differences, but the following may be taken as a fair aver- 

 age: Carbon, 50 per cent; nitrogen, 16 per cent; hydrogen, 7 per cent; oxygen, 22 

 per cent; sulphur, 0.3 per cent; phosphorus, 0.4 per cent.^ 



The nitrogen requirements and the means by which these are met constitute a 

 fundamental phase of bacterial, as well as all other plant and animal metabolism, and 

 the problem of nitrogen supply in the best available form is one that greatly con- 

 cerns all living organisms. 



Bacteria may to a large extent be classified on the basis of physiological activities. 

 Jensen believes that this is the only logical criterion. We speak of different groups as 

 the nitrifying, proteolytic, putrefactive, lactic acid producing, etc., groups, or as those 

 of the sulphur or iron bacteria. 



With respect to nitrogen utilization alone bacteria often reveal the widest differ- 

 ences, and numerous processes of nitrogen transformations may be observed, even in 

 the same organism. The two main processes, however, are those of katabolism or 

 analysis, and anabolism or synthesis. As this paper deals with protein metabolism, 

 the first of these two processes may be discussed under the following head. 



PROTEOLYSIS AND PUTREFACTION 



Cell metabolism involves a complex system of interchange of chemical substances 

 between the cell and the surrounding medium. The work of Lubbert^, Hesse,^ and 

 others, and more recently that of Novy,^ has shown that bacterial cells engage in a 

 process of true respiration and that a respiratory coefficient may be established for 

 different organisms. Gotschlich^ gives the coefficient as 0.71-0.78 (CO2: O2) in the 

 absence of fermentable (sugar, etc.) substances. Novy found the coefficient for the 

 tubercle bacillus to be 0,836, when grown on glycerol agar. 



' Seibert, F. : Science, 66, 433, 1927. 



^Mathews, A. P: Physiological Chemistry, p. 109. New York, 1922. 



^Liibbert,: Biologische Spaltpilz Uniersuchungen, p. ^S. 1886. 



''Hesse, W.: Zischr. Hyg. u. Infektionskrankh., 15, 17. 1893; 25, 477. 1897. 



5 Novy, F. G.: J. Infect. Dis., 36, 168. 1925. 



^ Gotschlich, E.: Kolle and Wassermann, Handb. d. Path. Mikroorg., i, 99. 1912. 



