68 



the purine and pyrimidine compounds of these nucleic acids, as 

 well as the lecithins (Aso 1904, Stoklasa 1911) and nitrogenous 

 lipins and nitrogenous acids would be precipitated with the true 

 humin by the calcium hydroxide. 



The basic nitrogen figures are not widely divergent although 

 there may be some significant differences. The differences be- 

 tween the nitrogen in the filtrate from the bases is perhaps the most 

 significant of all. An amino nitrogen of only 17.11 per cent in the 

 filtrate from the bases such as is found in the hydrochloric acid 

 extract is far lower than has ever been obtained in an analysis 

 of a pure protein and indicates that the nitrogen of this extract is 

 essentially non-protein. 



Unfortunately it was impossible to complete the corresponding 

 analyses on the calcareous black grass-peat, but the fractions ob- 

 tained would indicate a distribution similar to that of the sphagnum- 

 covered peat. 



H. General conclusions in regard to the distribution of soil 

 nitrogen in different soil types. From a study of Table XXVI we 

 observe a great similarity between the different fractions. This is 

 practically the same deduction made by Potter and Snyder (1915 a) 

 in regard to their study made on a single soil type under different 

 fertilizer treatment. 



I find that the nitrogen distribution in a soil is very uniform 

 whether in the same soil type under different fertilizer treatment, 

 or in different soil types. This is to be expected, for if one were 

 to take fifty Van Slyke analyses of protein at random and compare 

 the average analyses with that of another fifty analyses, one should 

 expect to find results agreeing closely with each other. This 

 expectation should also hold true for the hydrolysate of soils, since 

 in each soil are to be found many of the nitrogenous compounds 

 contained in the plant and animal products that find their way 

 to the soil together with their decomposition products. Since 

 there is such a great variety of different nitrogenous substances 

 in the soil, it stands to reason that the nitrogen distribution in 

 soils is an average distribution, and as such should not be ex- 

 pected to vary widely from soil to soil. 



It has been shown in the earlier part of this discussion that 

 when fibrin was hydrolyzed in the presence of ignited subsoil, no 

 histidine fraction was obtained. 



For reasons which were stated previously, I have not tabu- 

 lated the nitrogen distribution under the different headings used 

 for the analysis of pure proteins. However, in view of the results 

 obtained on the fibrin hydrolyzed in the presence of ignited sub- 

 soil, it is perhaps worth while to consider what values the histidine 

 fraction would have had. The Fargo clay loam, Fargo silt loam, and 

 Sample I of the Carrington silt loam, gave results indicating that 

 this fraction was absent, while Sample II of Carrington silt loam 

 gave 2.97 per cent, Hempstead silt loam 0.78 per cent, prairie-cov- 

 ered lo.ess 1.21 per cent, and forest-covered loess 1.25 per cent of 

 histidine nitrogen. 



