1923] 



KLOTZ — NITROGEN METABOLISM IN FUNGI 



345 



days. The determinations, moreover, corroborate those of Dox 

 and Maynard ('12 and '13). 



While it is not known that NIL is an end product of protein 

 metabolism, it is certain that it is directly related to autolytic 

 processes; and in cultures where peptone or protein is the sole 

 source of C and N, NHi is produced in excess by the breaking 

 down of large numbers of molecules and the use of the non-N- 

 containing parts for energy. In the experiment on N fixation 





Fig. 5. Dry weights of fungous mats. Aspergillus niger, first series. 



reported at the beginning of this discussion, it is significant that 

 the N content of the cultures remained constant for 29 days. 

 The initial N content of the media was very small, and any 

 ammonia formed from the peptone in the presence of the abun- 

 dant sugar was immediately reassimilated and retained. There 

 was consequently no loss of N during 29 days of incubation. On 

 the other hand, in the cultures of Sphaeropsis and Diplodia where 

 the peptone content was large and the sugar disappeared in 

 7 to 8 days, there was a distinct loss of nitrogen when the cultures 

 became alkaline. The strong odor indicated that the loss was 

 due to the evolution of free NH$. At the end of 15 days a culture 



