FIXATION OF NITROGEN BY FUNGI 



187 



The method used by myself had the special advantage that 

 exactly the same standard was used throughout; i.e., the same 

 identical solution from which the supply of nitrogen was taken 

 for the cultures, in the beginning, was used as the standard for 

 Nesslerization at the end. No such rigid test or standard is 

 possible in the titration method and ordinarily would not be 

 observed in the colorimetric method. 



TABLE 5 



Experiment D. Aspergillus cultures in Czapek's solution containing 5% dextrose. 

 Each culture containin,g 5 cc. of the solution, to which was added either 1 cc. or 

 2 cc. of the ammonia solution 



The blanks kept with this set were not analyzed since those kept and analyzed 

 in the other experiments showed no gain and further because it was decided at 

 this point to abandon the use of controls containing nutrient solution for reasons 

 stated in the text. 



TABLE 6 



ExperimeJit E. Aspergillus cultures in Czapek's solution mth 2.5% sodium 

 citrate and 2.5 dextrose. Each culture containing 5 cc. of the solution, to which 

 was added 1 cc. or 2 cc. of the 1 mgm. ammonia solution 



In order to insure that the chemicals used, both in the culture 

 and in the analyses, should be pure and free from nitrogen, 

 except when its presence was desired, numerous blanks were 

 run from the supplies. 



The most likely source of error of this character would be in 

 the carbohydrates furnished, as these are used in larger quan- 

 tities than any of the other ingredients. Only the best brands 



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