QUANTITATIVE MEASURE OF BACTERIAL METABOLISM 79 



position of purely nitrogenous substances by bacteria; they furnish 

 quantitative evidence of the extent of the utilization of carbohydrates 

 by bacteria in preference to nitrogenous substances for fuel (catabolic) 

 purposes; that is to say, such measurements evaluate the nitrogen 

 metabolism of bacteria in purely protein solutions, and their nitrogen 

 metabolism in media containing both protein and utilizable carbo- 

 hydrate. 



Such determinations have been made for a large series of bacteria 

 by Kendall and Farmer, 1 and Kendall, Day and Walker. 2 The gen- 

 eral method followed is to measure the amount of ammonia (deamin- 

 ization) which appears in fluid cultures of bacteria under various 

 conditions of growth. The following table shows, respectively, the 

 change in reaction (to neutral red as an indicator in terms of T acid 

 or alkali per 100 c.c. media) and the increase in ammonia (milli- 

 grams per 100 c.c. media), as certain bacteria are grown for ten days 

 in plain and dextrose broth respectively. The broths are identical 

 in initial composition and reaction, except that the "dextrose broth" 

 contains in addition to the ingredients of the "plain broth" 1 per cent, 

 of chemically pure dextrose. All other conditions are exactly parallel. 

 The results are averages of several strains of the same organism in 

 various lots of media. It will be seen that B. alcaligenes, for example, 

 which ferments no sugars, produces an alkaline reaction (indicated 

 as " " in the table) both in plain and dextrose broth: the amounts 

 of ammonia in both media are nearly the same. 



All the organisms which ferment dextrose produce less ammonia 

 in the dextrose medium than in the corresponding sugar-free medium, 

 although the numbers of living bacteria were found to be greater in 

 the former than the latter. The small amount of ammonia in the 

 dextrose broth appears to be largely the nitrogenous waste incidental 

 to the utilization of protein for structural purposes: the relatively 

 large amount of ammonia observed in the corresponding sugar-free 

 broths is the combined "structural waste" and the " deaminization" 

 incidental to the utilization of protein for their energy requirement. 

 The progressively pathogenic bacteria, as the diphtheria, typhoid 

 and dysentery bacilli, produce much Ies3 ammonia in sugar-free 

 media than do the same organisms in various lots of media. 3 (Kendall, 

 Day and Walker.) 



1 Jour. Biol. Chem., 1912, xii, 13, 215, 219, 465; xiii, 63. Methods ^iven here. 



2 Jour. Am. Chem. Soc., 1913, xxxv, 1201-1249. 



3 Ibid. 



