1923] 



KLOTZ — NITROGEN METABOLISM IN FUNGI 



353 





Aspergillus niger. The media which were made strongly acid 

 by the fungi produced mats having the highest N percentage. 

 This is possibly due to the inhibiting action of the H ion on 

 autolysis. The media on which the fungi made the fastest and 

 largest growth yielded mats having the lowest per cent of N. 



The behavior of the 3 fungi in the (NH^jSO* medium was 

 similar in that all increased the acidity of this solution. The 

 greatest hydrion concentration was produced by Aspergillus 

 niger; the maximum acidity (P H 1.9) appeared in 3 days, after 



i *> 





KNQj~ 



Fig. 13. Ammonium N in 50 ml. media. Aspergillus niger, second and third series 



+ 



which time there was a slight decrease in 

 P H 2.3-2.4. This decrease is synchronous with the disappearance 

 of the sugar, the beginning of a decrease in the weight of the 

 fungous mat, increase in the total and ammonium N from a 

 minimum, and appearance of a trace of amino N in the medium. 

 The maximum acidity reached is due to the sulphuric acid freed 

 from the (NH ») »H 2SO4 plus the organic acids formed in the decom- 

 position of the sugar, the decrease of acidity to the consumption 

 of the organic acids and also to autolytic processes. The iodine 

 test for soluble starch gave a negative result after 4 days of in- 

 cubation but a strongly positive test after 20 days. A similar 

 course of reactions takes place in the cultures of A . niger on the 



