PROTEOLYTIC ACTIVITIES OF SOIL MICROORGANISMS 491 



of amino nitrogen in the medium and a comparatively smaller 

 accumulation of ammonia. 



4. The growth of A. niger upon a solution containing peptone 

 shows that the amino nitrogen produced in the medium is used 

 up by the organism, so that no great accumulation takes place. 

 Ammonia, on the other hand, which seems to be a waste product 

 of the metabolism of the organism, accumulates readily in the 

 medium, particularly when the organism stops growing and 

 begins to autolyze. 



5. The presence of available carbohydrates checks the ac- 

 cumulation of ammonia in the medium, due to the fact that in 

 their presence the organism uses only as much of the protein 

 molecule as it needs for its nitrogen metabolism, and only a small 

 quantity of aimnonia will accumulate. 



6. The process of ammonification, in the presence of available 

 carbohydrates, is found to be an autocatalytic chemical reaction. 



7. In the absence of available carbohydrates, the observed 

 data deviated from the data calculated by the use of the curve of 

 autocatalysis. 



8. The study of ammonification is of doubtful importance in 

 revealing to us the proteolytic activities of microorganisms, since 

 the quantity of ammonia accumulated in the medium depends 

 on a great number of controlling factors; it has not been proven 

 as yet that ammonia is an end product of protein metabolism. 



9. Asparagine nitrogen is rapidly converted into ammonia 

 nitrogen, after the organism has made its maximum growth; 

 but, where the amount of asparagine nitrogen is small, particularly 

 in the presence of a comparatively large excess of available 

 carbohydrates, no ammonia or only a very small quantity of it 

 will accumulate in the medium. 



The writer wishes to express his most sincere thanks to Dr. 

 T. B. Robertson and Dr. C. B. Lipman, of the University of 

 California, for reading the manuscript. The second part of this 

 paper, dealing with the proteolytic enzymes of soil fungi and 

 actinomyces will be published later. 



