19231 



KLOTZ — NITROGEN METABOLISM IN FUNGI 



329 



the time and trouble required to clean and renew the material 

 and in adding the NaCl and MgO, together with the necessity of 

 running blanks without couple where the solution contained 

 NH<.N, made it inadvisable to use this method. The difficulty 

 of the proper execution of the old gasometric method of Schulze- 

 Tiemann (Emmerling, '12) is recognized by those who have em- 

 ployed it. The method of Strowd ('20) was adopted because of 

 its simplicity and its fair degree of accuracy. In this the nitrates 

 are reduced to NIL by means of Devarda's alloy in the presence 

 of alkali, blanks with alkali but no alloy being ' ' run ' ' at the same 

 time under as nearly similar conditions as possible. This did not 

 give dependable results, however, in the presence of dextrose, 

 the sugar in some way holding back some of the nitrate. Ac- 

 cordingly the results obtained with media containing sugar, as 

 given in the following data, are not considered reliable. The 

 results obtained in the third series with Aspergillus niger are 

 shown in the graphs (fig. 10), because they indicate relatively the 

 course of nitrate consumption by this fungus ; moreover, the sugar 

 being entirely consumed by this organism in 5 days, the results 

 for nitrate carry more weight. In subsequent series the nitrate 

 was determined only after the disappearance of the sugar, and the 

 results given were obtained by subtracting the result for NH, 

 from that for total N. 



Nitrites were determined in the first series with Aspergillus 



niger, a "micro" 



modification of the official method 



1 Official Methods ') , as applied to water analysis, being developed 

 and used. In the official method the color ratios are obtained 

 by varying, in 1 ml. quantities or multiples thereof, the amount 



of standard nitrite in the 

 standard containing 0.0001 mgm. of 



ml. of HjO, each ml. of 



9 



nitrite. The same auan- 



of reagents are added to each tube of standard and unknown. 

 In the " micro" method the proportions of standard nitrite to 

 5 ml. water were maintained by use of a pipette that delivered 

 20 drops per ml. It is seen, therefore, that each drop of standard 

 nitrite in 5 ml. of H iO corresponds to the 1 ml. of standard nitrite 

 in 100 ml. of HjO. The standards were made in small, sero- 

 logical test-tubes marked at 5 ml. The same corresponding 

 amounts of the reagents (concentrated HC1 diluted 10 times, 



