476 • SELMAN A. WAKSMAN 



enumerate all the work that has been done along these lines, 

 particularly the so-called "ammonification" studies. The fact 

 is almost decided upon that the microorganisms decompose the 

 organic matter in the soil, liberating ammonia, which is oxidized 

 by other groups of organisms to nitrites, and then to nitrates, 

 in which form it is utilized by higher plants. Several investi- 

 gations seem to point to the fact that, in the absence of nitrates, 

 other compounds, such as certain amino-acids, as shown by Skin- 

 ner (1912a) and Brigham (1917), creatinine, studied by Skinner 

 (1912b) and Brigham (1917), amides and ammonium salts, as 

 shown by Hutchinson and Miller (1912), and other organic 

 compounds (Brigham, 1917) can also be utilized by plants. 



Very little work has been done on the process of decomposition 

 of proteins as such, taking into consideration the intermediate 

 steps and finding out whether the ammonia and other substances 

 formed are merely products of metabolism or are final decom- 

 position products. The organisms themselves must be studied, 

 so as to learn by what biochemical processes the work is accom- 

 plished and what ends are attained, and only thus shall we be 

 able to learn how to utilize the microorganisms for our needs in 

 the economy of the soil and in other lines of human endeavor. 



HISTORICAL 



The work of Fisher and his followers, having firmly established 

 the general structure of the protein molecule, has given a great 

 impetus to the study of the hydrolysis and the synthesis of pro- 

 teins by chemical and biological means. A great many investi- 

 gations have been made of the action of bacteria and molds on 

 proteins. It has been conceded that a great deal of this work 

 is done by enzymes, but most of the data at hand are merely 

 qualitative in nature, and few investigators have obtained de- 

 finite quantitative information concerning the action of micro- 

 organisms or their enzymes upon protein compounds. 



It has not been decided as yet, what nitrogen compounds form 

 the Bausteine for these organisms. Czapek (1902) and others 

 have shown that amino-acids form a much better source of nitro- 



