478 SELMAN A. WAKSMAN 



tures of most bacteria give fluctuating concentrations of amino- 

 acids, as measured by the Van Slyke apparatus ; these bodies are 

 formed and broken down continuously by the organisms, with 

 the exception of a few strongly proteolytic bacteria; while the 

 ammonia gradually accumulates in the medium, the amino-acid 

 content fluctuates daily and gradually decreases in most instances. 

 Itano (1916) using the formol-titration method of Sorensen 

 has shown that B. suhtilis produced a gradual increase of formol- 

 titrating nitrogen for a period of 240 hours. The greatest pro- 

 teolysis took place toward the optimum hydrogen-ion concen- 

 tration; therefore he suggested the probability that the enzyme 

 is tryptic-like in nature; on filtering the bacterial cultures, he 

 obtained no splitting of the peptone with the filtrate, but did 

 obtain it with the bacterial mass. 



These proteolytic changes are very important in the study of 

 soil fertility. Schreiner and Shorey (1910) isolated from the soil, 

 among numerous other organic compounds, the amino-acids 

 histidine, arginine, and lysine, using a weak alkali extract of 

 soil. That these amino-acids can be utihzed by the plants as 

 well as nitrates is seen from the work of Skinner (1912a), who 

 has shown that histidine and arginine have a beneficial effect 

 upon plant growth and can replace nitrates. 



A great deal of work has been done on the production of am- 

 monia from different organic compounds through the action of 

 microorganisms, but no attempt will be made to review that work 

 in this paper, because the study of "ammonification" is thought 

 to be of doubtful importance, as a factor in the fertility of the 

 soil or activities of microorganisms, when the other factors con- 

 trolling these activities are not taken into consideration. 



EXPERIMENTAL 



Organisms used 



Aspergillus niger van Tieghem. This organism was isolated 

 on the College Farm, at New Brunswick, N. J., from a Sassafras 

 sandy loam that was under orchard for over twenty years. 

 Methods of isolation and the description of soils for this as well 



