1 86 SOIL CONDITIONS AND PLANT GROWTH 



or so varieties that invariably occurred, practically all de- 

 composed the albumin and formed ammonia. One of the 

 mycoides group proved very vigorous and was studied in some 

 detail. The process was considered to be a simple oxidation 

 necessary to the life of the organism ; oxygen was absorbed 

 and carbon dioxide evolved, the ratio NHg : COj produced 

 being i : 8'9. For complete oxidation of the carbon, hydro- 

 gen, and sulphur of the albumin molecule the ratio would be 

 1:10-3; but the change was known to be incomplete, and 

 small quantities of leucine, tyrosine, and fatty acids could 

 also be detected. Free oxygen, however, was hot essential. 

 When grown in a culture solution containing sugar and nitrate 

 the organism took its oxygen from the nitrate, but it still 

 produced ammonia. 



The energy relationships thus indicated were wholly over- 

 looked by investigators for nearly a quarter of a century : it 

 was not till 1 91 6 that Doryland (86) showed their significance. 

 The organism produces ammonia, not because it must, but 

 because it can do so, and can leave ammonia in excess of its 

 needs : its prime requirement is energy. If sources of energy 

 other than proteins are supplied, e.g. carbohydrates, these may 

 be used and then there is a decrease in ammonia production 

 which may finally fall to nothing or become negative : the 

 ammonia producers then become ammonia absorbers just 

 like the higher plants, and indeed they compete with growing 

 crops. It follows that no simple numerical expression can 

 be given for the ammonification of organic matter : the true 

 constant is the requirement of energy. This might be ex- 

 pressed in terms of protein if no other carbon compounds 

 were present, but it is improbable that any equivalent could 

 be worked out for the complex mixture in ordinary soils. ^ 



^ For other experiments on the effect of carbohydrate in reducing ammonia 

 production see H. M. Jones, J. Infect. Dis., 1919, 19, 33, showing that Bac- 

 proteus does not produce a proteolytic enzyme in presence of available carbo- 

 hydrate ; J. G. Lipman and Blair, New Jersey Bull., 247, 1912, and Annual Rept., 

 1914, p. 220, ammonia producing power of soil is diminished by carbohydrates ; 

 S. A. Waksman, J.Amer. Chem. Soc, 1917, 39, 1503, similar effects are produced 

 in cultures of aspergillus ; I. J. Kliger, Jour. BacL, 1, 663, and Berman and Rettger, 

 Jour. Bad., 1918, 3, 389. 



