ENERGY AND NITROGEN TRANSFORMATION 505 



substances to the protein, the smaller is the amount of ammonia liber- 

 ated. This has an important bearing upon the liberation of ammonia 

 in the soil, since the great mass of organic matter usually added to 

 ^he soil, in the form of manures and plant residues, contains a low 

 per cent of nitrogen and a high per cent of energy-yielding material. 

 The available nitrogenous plant food in the soil is also greatly affected 

 by the conditions under which decomposition takes place, since, under 

 different conditions, different organisms will take part in the process 

 and will, therefore, bring about different sets of reactions. Microorgan- 

 isms vary in the amount of carbon reassimilated, in the relative nitro- 

 gen content, and in the nature of decomposition that they bring about. 



Influence of non-nitrogenous organic matter upon the decomposition of 

 nitrogenous compounds and upon the amounts of ammonia liberated. 

 The presence of non-decomposed or only partly decomposed non- 

 nitrogenous organic matter in the soil modifies in various ways the 

 decomposition of nitrogenous compounds by microorganisms, by 

 influencing the amount and the nature of decomposition. 



Hirschler 1 was the first to point out that the decomposition of pro- 

 teins by microorganisms is modified by the presence of carbohydrates 

 which prevent the formation of aromatic products of putrefaction. 

 Indol, phenol, and oxy-acids were not formed in the decomposition of 

 proteins by bacteria when sucrose, starch, dextrin, glycerol or lactic 

 acid are present; i.e., the presence of an available source of energy 

 modified the decomposition processes. It was later 2 demonstrated 

 conclusively that bacteria do not decompose large amounts of proteins 

 in the presence of available carbohydrates; the amount of ammonia 

 formed may also be greatly diminished. This is due to the fact that 

 the organisms derive their energy preferably from carbohydrates and 

 act upon the proteins only to an extent sufficient to obtain the nitrogen 

 required for the synthesis of their protoplasm. Any ammonia that 

 is produced, in this connection, may be reassimilated. In the absence 

 of available carbohydrates, proteins are used also as sources of energy 

 and large amounts of nitrogen are liberated as waste products in the 



1 Hirschler, A. Uber den Einflusz der Kohlehydrate und einiger anderer 

 Korper der Fettsaurereihe auf die Eiweissf iulniss. Ztschr. physiol. Chem., 

 10: 306-317. 1886. 



2 Kendall, A. I. The significance and quantitative measurement of the nitroge- 

 nous metabolism of bacteria. Jour. Inf. Dis., 30: 211. 1922; also Ibid., 17: 

 442^53. 1915; Jour. Amer. Chem. Soc, 35: 1201-1249. 1913; 36: 1937-1962. 

 1914. 



