63 



It is possible that the specific character of the histidine nitro- 

 gen is destroyed by certain oxidizing agents present during the 

 hydrolysis, with the result that histidine nitrogen is not precipi- 

 tated in the basic fraction. A study is being conducted at the pres- 

 ent time on the hydrolysis. of pure protein in the presence of certain 

 inorganic oxidizing agents. It is hoped that some light will be 

 thrown upon the disappearance of histidine as well as the formation 

 of "humin" and of the ''nitrogen precipated by calcium hydroxide." 



It is of interest to note that the average total nitrogen in the 

 two samples in Table II is 0.4584 gram (cf. Gortner 1916 c, where 

 total nitrogen on four determinations of three grams averaged 

 0.4551), showing that all of the nitrogen present is accounted for 

 in the method of analyses used. 



Table IV shows the difference between the duplicate deter- 

 minations of the analysis of fibrin alone and in the presence of car- 

 bohydrate and of subsoil, and the differences apparently due to the 

 addition of 100 grams ignited subsoil to the 3 grams of fibrin. Van 

 Slyke's (1911) "maximum" and "average" differences to be ex- 

 pected between duplicate determinations are also given in the table 

 for reference. 



From a study of Table IV it will be seen that the difference 

 between the analyses of fibrin hydrolyzed alone and in the presence 

 of ignited subsoil are, in the case of most of the fractions, within 

 the maximum allowed by Van Slyke for experimental error. The 

 only differences which are certainly greater than experimental 

 error are those of humin nitrogen, histidine 1 nitrogen, and amino 

 nitrogen in the filtrate from the bases. It is observed that prac- 

 tically the same error occurred with the amino nitrogen in the fil- 

 trate from the bases when hydrolysis was carried out in the pres- 

 ence of carbohydrate. 



From this analysis one can only draw the conclusion that even 

 if the organic matter of the soil consisted entirely of pure protein, 

 one would not obtain the same nitrogen distribution by the Van 

 Slyke analysis in the presence of soil that one would obtain in the 

 cibsence of the soil, or in other words, the presence of ignitied min- 

 eral subsoil intefferes with the Van Slyke analysis in much the 

 same manner as carbohydrates (Gortner 1916 c, and Hart and Sure 

 1916). 



B. The humin nitrogen, its origin and significance. In such 

 a discussion one must first consider the source of humin nitrogen 

 in pure proteins. 



Osborne and Jones (1910) suggest that perhaps tryptophane 

 and histidine are responsible for the humin formation, basing their 

 pbsttilation on the fact that zein, which contains no tryptophane 

 and but little histidine, gives only small amounts of humin on 

 hydrolysis. 



Gortner and Blish (1915) hydrolyzed zein in the presence of 

 both tryptophane and of histidine and found that a large part of 

 the tryptophane was converted into humin nitrogen, whereas none 



