188 CHARLES OSCAR CHAMBERS 



of chemically pure stock were used, as they alone would be re- 

 liable. 



It seems highly probable that some of the gains shown in the 

 work of Puriewitsch were derived from his carbohydrates; 

 in fact he admits that in the preliminary tests of his culture 

 media the nitrogen was higher than it should be by theoretical 

 calculations. He attributes the error to N-compounds in the 

 sugar which he used. Consequently it would be expected that 

 with increase of sugar there would be a proportional increase of 

 apparent gain in nitrogen as given in his results. The same was 

 true of Stahpi and of Frohhch.^^ 



In my work the amount of chemicals used, other than carbo- 

 hydrates, was so small that the danger of contamination from 

 the other chemicals was very small. Also, in the analysis by 

 the micro-method such small amounts of chemicals are required 

 that it is possible to keep them scrupulously tested and protected 

 against contamination much more efficiently and easily than in 

 the other methods. 



Triply-distilled water was used in making culture solutions, 

 after the first preliminary sets, and specially distilled water was 

 used in all the analyses, having been shown by tests to be abso- 

 lutely free from ammonia. The nitrogen supply furnished in the 

 culture-media was taken in the ammonia form, ammonium 

 sulphate (NH4)2SO^, because it gave normal growth, as shown 

 by Nitinsky^^ and Czapek.^^ Also, this form presented no diffi- 

 culties in the digestion process such as would be met with in the 

 use of nitrates. 



Dextrose was finally adopted as the source of carbohydrate 

 largely because it is stated by a number of investigators, includ- 

 ing Czapek, Frohlich, and Lipman to give the best growth with 

 Aspergillus. The dextrose which I used bore the mark of 

 Merck. The other chemicals bore the name of Baker and 



-' Stahel, G., Stickstoffbindung durch Pilze bei gleichzeitiger Erniihrung mit 

 gebundenen Stickstoff. Jahrb. f. wiss. Bot. 49: 579-615. 1911. (See p. 599). 

 " Frolich, I. c. 



" Nitiusky, I. c, pp. 17 and 33. 

 " Czapek, I. c, p. 138. 



