PROTEOLYTIC ACTIVITIES OF SOIL MICROORGANISMS 477 



gen for fungi than other nitrogen compounds. Hence he argued 

 that since the fungi must build their own proteins out of the 

 ammonium compounds and nitrates through the amino-acid- 

 stage, if the latter is offered to the organisms as a source of nitro- 

 gen, it is assimilated as such and the organism is spared un- 

 necessary loss of energy, which it would have to spend in the 

 building up of these amino-acids. Abderhalden and Rona (1905) 

 have shown that when KNO3, glutamic acid, and glycocoll 

 are offered to the organisms as sources of nitrogen, the proteins 

 that are built up will contain the same amino-acids in all cases, 

 namely glycocoll, alanine, leucine, glutamic and aspartic acids. 

 Hence they argued that the nitrogen buildiDg stones for these 

 organisms must be ammonia; all the nitrogen compounds must 

 be first split into ammonia, and out of this form of nitrogen all 

 the proteins are built up, going through the amino-acid stage. 

 Hagem (1910) supported the claim of Abderhalden and Rona 

 (1905) by showing that the oxy-acids of ammonia are utilized 

 just as well by the fungi as amino-acids; therefore he thought 

 that in the case of amino-acids, both the nitrogen and carbon 

 are utilized by the organism: the amino-acid is first split to 

 ammonia and oxy-acid; the ammonia is utilized for the nitrogen 

 needs, and the oxy-acids form a ready radical for the building 

 up of the numerous amino-acids which go to make up the fungus 

 protein. The oxv-acids of ammonia behave in a similar way, 

 therefore these compounds offer a better source of food to the 

 organism than other nitrogen compounds. 



Butkewitsch (1903) identified tjrrosine and leucine among the 

 amino-acids produced by the action of Aspergillus niger and 

 Mucor stolonifer upon peptone. Rettger and his associates 

 (1916) have shown that bacteria are unable to attack or bring 

 about the decomposition of proteins without the aid of enzymes 

 or other proteolytic agents; this applies not only to the more 

 complex proteins, like egg-albumen, but in all probability to 

 albumoses and peptones as well. A wider range of ability to 

 attack nitrogenous substances is observed for molds, as can be 

 seen from the work of Czapek (1902) Emmerling (1902), Brenner 

 (1914), and others. Sears (1916) has shown that peptone cul- 



