1923] 



KXOTZ — NITROGEN METABOLISM IN FUNGI 



325 



collected 



the volumetric flask with the culture solutions. 



Aliquot portions of the filtrate and washings, which were made 

 to volume and thoroughly mixed, were used for the determinations 

 enumerated above. 



The fungous mats were dried at 100-105° C. in an electric 

 oven, cooled in a desiccator, and weighed to the nearest milligram 

 on a "chainomatic" balance. 



The active acidity of the culture solution was determined 

 colorimetrically by employing the indicators and buffer solutions 

 suggested by Clark and Lubs ('17) and Clark ('20). A com- 

 parator blank was used throughout. Near the ends of the ind- 

 cator ranges it was helpful to make use of the colorimeter (Duggar 

 and Dodge, '19), as this instrument extends the range and use- 

 fulness of an indicator. The micro Duboscq instrument can be 

 applied very satisfactorily to this work by following these meas- 

 urements. Two ml. of unknown plus 2 drops of indicator should 

 be placed in the lower right cup, and in the cylinder above this 

 .625 ml. of H 2 0. In the left cup and cylinder should be placed 

 respectively the corresponding quantities of known buffer plus 

 indicator and compensating unknown solution. The readings 

 are made at the 16.5th graduation in order to obtain like columns 

 of colored solution and compensating solution. 



Various methods for determining reducing sugars were tried. 

 The results reported in the first series with Aspergillus niger 

 were obtained by direct titration of the culture solution against 

 Fehling's solution, the various indicators used to determine the 

 absence of Cu and end point of the titration being tried. The 

 1920 iodometric method of Shaffer and Hartmann ('20) was 

 found most satisfactory as it is accurate and rapid. The Feh- 

 ling's modification was used throughout for " macro" quantities 

 of sugar, as closer checks could be obtained with this than with 

 the carbonate-citrate reagent. The advantage of the latter in 



having the chemicals combined in a single solution is outweighed 

 by the increased cost and by the danger of loss of material from 

 foaming when the solution is acidified at the end of the reduction. 

 The "micro" method described in that paper was used in the 

 second and third series with Aspergillus niger when the con- 

 centration of the glucose became sufficiently low; it was used in 



