PROTEOLYTIC ACTIVITIES OF SOIL MICROORGANISMS 489 



asparagine molecule for the utilization of the carbon part of it, 

 thus leaving the nitrogen in the medium as ammonia. 



Ammonia is usually looked upon as a final product in protein 

 metabolism. That this is not the fact has recently been pointed 

 out by Berman (1916), who stated that the determination of 

 free ammonia as an index of protein metabolism should be con- 

 demned. As a matter of fact we have very little knowledge on 

 that point. The accumulation" of ammonia in the medium is 

 probably due to several causes: firstly, it is an important waste 

 product in the nitrogen metabolism of microorganisms ; secondly, 

 it is possible that, for certain organisms at least, the proteins and 

 other nitrogenous substances must be first broken down to am- 

 monia, this being assimilated as such by the organism, although 

 we have no direct evidence on that point ; in such a case the organ- 

 ism may split off more ammonia than it can use, so that a great 

 deal of it is left in the medium. The fact that ammonia is not the 

 final product of protein metabolism can be demonstrated in the 

 case of those organisms that accumulate a large quantity of amino 

 nitrogen, as was shown for P. chrysogenum, Act. penicilloides, 

 Act. violaceus-ruher, and B. mycoides. Or it is possible that the 

 different microorganisms behave differently in this respect, and 

 the ammonia which may be only a waste product for some organ- 

 isms may act as an intermediate product for others. 



The problem of proteolytic activities of microorganisms is not 

 such a simple one as might be thought at first. Most bacteri- 

 ologists limit themselves to the study of one particular nitroge- 

 nous product, usually ammonia, and thus conclude that they are 

 studying protein metabolism, often without taking into consider- 

 ation the numerous controlling factors. In a number of experi- 

 ments on amjnonification in the soil by the so-called "beaker 

 method," the author was able materially to alter the ammonia 

 produced from a certain organic substance, using the same soil, 

 the same moisture content, temperature and period of incubation, 

 so as to have all the environmental conditions as much alike as 

 possible, and merely changing one factor, such as the size of the 

 soil particles: when the soil was placed in the beaker in small 

 lumps, the greater aeration allowed a better development of the 



