1923] 



KLOTZ — NITROGEN METABOLISM IN FUNGI 



313 



reaction adverse to the decomposition of the amino acid. In the 

 presence of a good C source NH« was found a better N source for 

 the fungus than single amino acids, but a suitable mixture of 

 amino acids was better than NH«. 



In his severe criticism of the opinions of Czapek, Puriewitsch 

 Brenner, and others on the direct usability of amino acids, Boas 

 ('18) pointed out the fallacy of attempting to judge the com- 

 parative assimilability of N nutrients under the widely varying 

 conditions of experimentation employed by those workers. For 

 example, a hydrochloride of guanidine could not satisfactorily 

 be compared with an amino acid because of the liberation from 

 the former under the action of a fungus of an abundance of the 

 inhibiting acid, HC1. He emphasized the necessity for corn- 



am 



compounds at the same hydrion concentration; for 

 in the comparison of asparagin and (NH 4 ) 2 SO«, 



, the 



production of soluble starch and delay in sporulation observed 

 with the latter compound, and which indicated an abnormal 

 metabolism, resulted from or was conditioned by the liberation 

 of HjSO*. Czapek, in his choice of incubation periods of 21 days 

 or longer, it was pointed out, entirely ignored the effects of pro- 



teolysis on the fun 



crops. Boas then repeated Czapek 



experiment with guanidine, urea, and biuret, making weighings 

 of the fungous crop, at different time intervals and obtained a 

 reversal of the order of assimilability. The free acid liberated 

 from the guanidine-HCl, it was thought, inhibited autolysis so 

 that a long incubation period eventually gave a larger crop. 



Puriewitsch was also criticized on the same basis 



explained 



that the energy quotient would be a valuable index of the as- 

 similability of N compounds, if due regard were given to the use 

 of a variety of C sources, to the hydrion concentration of the 



medium 



the formation of soluble starch 



the effects of 



and to the influence of outer conditions, as tempera 



light, humidity, and 



He then 



periments. Mannite, glycerine, malic acid, and quinic acid were 

 employed as C sources, because, as he showed, the liberation of 

 acid from the ammonium salts of the strong acids did not upset 

 the carbon metabolism of the fungus when these compounds 

 were used ; soluble starch was not formed and there was no delay 



