218 LAURENCE F. FOSTER 



hydrate and protein for katabolic purposes will attack the former 

 in preference to the latter (Kendall and Farmer, 1912a, 1912b). 

 This phenomenon, which has been established by Kendall and 

 his associates as a fundamental principle of bacterial metabolism, 

 may be expressed concisely, according to Kendall and Farmer 

 (1912d) in the statement that, "Fermentation takes precedence 

 over putrefaction." These authors define fermentation as, ''The 

 action of microorganisms upon carbohydrates, putrefaction as 

 the action of microorganisms upon nitrogenous substances." 

 They state further that "The products of proteolytic activity, 

 which are only formed when bacteria are utilizing protein for 

 fuel are alkaline nitrogenous substances; the products of fermen- 

 tation, on the contrary, which are formed when bacteria are 

 utilizing carbohydrates for fuel, are non-nitrogenous, acid 

 products." 



Inasmuch as nitrogen is the most important structural element 

 entering into the composition of the cell, a quantitative measure 

 of nitrogen degradation must form a very important step in the 

 study of cellular metabolism. In man, nitrogenous waste is 

 excreted from the body mainly as urea, but with bacteria, which 

 are known to excrete nitrogen principally as ammonia, urea, if 

 formed at all, would represent a product of intermediary meta- 

 bolism. This theory is borne out by the fact that certain bacteria 

 are able actually to utilize urea. 



Kendall and his associates (1913) have concluded after many 

 studies upon a variety of organisms that ammonia formation, 

 representing the final step in the degradation of proteins and protein 

 derivatives, is the best available index of proteolysis by bacteria. 

 Ammonia formation is considered by Kendall and Walker (1915) 

 to result from intracellular deaminization of assimilated protein 

 derivatives, incidental to their transformation into energy. 



Kendall, Day, and Walker (1913a) have estimated that the 

 amount of protein needed for structural purposes by the bacterial 

 cell is in aU probabihty exceeded by the amount wasted through 

 excretion. The combined structural needs and structural waste 

 are much less than the fuel needs and the fuel waste. Further, 

 the fuel requirements only cease upon the death of the organism, 



