19 



The base choline is also widely distributed in both plant and 

 animal tissues as well as being a decomposition product of lecithins. 

 It has been shown to exist in the soil. Choline yields neurine by bac- 

 terial decomposition, and both of these compounds break up into 

 trimethylamine. This substance may also be added to the soil from 

 other sources, both animal and vegetable. As noted above Stoklasa 

 (1911) obtained evidences of lecithin in the soil and Aso (1904) re- 

 ports small quantities of lecithin present in soils rich in organic mat- 

 ter. Choline has been isolated from soil (Shorey 1913). The tri- 

 methylamine reported by Shorey (1913) possibly had its origin 

 in the lecithin molecule and it may be that the dihydroxy-stearic 

 acid of Schreiner and Shorey (1908 a, 1909 a) and the mono- 

 hydroxystearic acid (Schreiner and Shorey 1908 a, 1909 a) had 

 the same origin. (For a discussion of the organic phosphorus of 

 the soil sec (iortner and Shaw 1917). 



F. Bacterial Processes Which Influence the Form of Soil Nitrogen. 



We know that the decomposition of protein substances can be 

 brought about through bacterial activity or by the agency of en- 

 zymes widely distributed in the vegetable kingdom. We should 

 expect any protein materials present in the soil to be subject to 

 the action of the above agencies. Viewed in the light of the 

 researches of Emil Fischer (1899-06) protein hydrolysis leads to 

 disruption of the complex molecule and the formation of simple 

 molecules, as represented in the following scheme* 



i' Di-amino acids 

 Mon-amino acids 

 Acid amides 



Fischer has shown that the amino acid combination in the pro- 

 tein molecule may be represented as follows: 



HO H H O 



I I! ! ! !J 



H.N-C-C N-C-C-O H 



I I 



R R 



O H 



The group II ! being known as the "peptid group." The 



-C-N 



nitrogen in this group is in the form of the imino (-NH) radical. 

 Upon hydrolysis each "peptid group" takes up a molecule of water 

 forming a free carboxyl (-COOH) group changing the imino group 

 into an amino ( NH 2 ) group. 



As the protein hydrolysis continues, the proportion of nitrogen 

 in the amino form increases until it reaches a maximum at com- 

 plete hydrolysis. It has been shown by Van Slyke (1910, 1911) 

 that the amount of amino nitrogen formed is a measure r bf the 

 hydrolysis of the protein substance. The amino acids derived from 

 protein degradation may be acted upon by the bacteria in the soil 

 and bring about chemical changes which depend largely on the 

 character of the organisms present. 



