EDITORIAL. 207 



large number of chemical compounds, not necessarily related, derived 

 unchanged from plant or animal remains, or resulting from the 

 breaking down of complex bodies in the plant or animal tissue, or 

 from changes brought about by bacterial activity in the soil. The 

 character of the organic matter of the soil is therefore determined by 

 the nature of the materials added to the soil and the character of de- 

 composition they have undergone. 



It is obvious that there can be no clear understanding of the func- 

 tions of the organic matter of soils without exact knowledge of its 

 composition. Such knowledge is important from the standpoint of 

 the farmer, but much more important from the standpoint of the 

 scientific investigator. On this point Schreiner says: "There can 

 be intelligent chemical treatment of any material only when the 

 chemical nature of the material treated is known. The treatment to 

 which soil organic matter is subjected under cultural methods is in 

 part at least chemical treatment in that such methods induce chemi- 

 cal changes. The operations of irrigation, conserving of moisture 

 by mulches, aeration by cultivation, inoculation with cultures of 

 bacteria, addition of organic and green manures, are all common agri- 

 cultural methods used by farmers and they are also operations that 

 influence the chemical changes which soil organic matter undergoes." 



The theor}' that humus is a more or less definite body, represent- 

 ing the valuable portion of the organic matter of the soil, has led to 

 much futile effort on the part of chemists to devise methods of isolat- 

 ing this body from soils and studying its properties with relation 

 to soil fertility. The rather limited results and possibilities of this 

 line of inquiry from a scientific standpoint have been brought out 

 by the work of a long list of investigators, as well as that of the As- 

 sociation of Official Agricultural Chemists, which, after a number of 

 years of comparative tests of various proposed methods for determin- 

 ing humus, voted at its last meeting " that the referee on soils for 

 1911 be instructed to investigate the subject of a more accurate 

 method for humus determination." 



It is evident from an examination of the work referred to, as well 

 as the various discussions of the subject which appear from time to 

 time, that no one knows in a scientific sense what humus is, or is able 

 to draw a clear line of distinction between humus and other organic 

 matter in the soil. It is therefore of fundamental importance to in- 

 ^estigate the organic matter of the soil as a whole and to isolate and 

 study the origin and properties of all of the definite organic com- 

 pounds which it contains. 



Greater progress has very recently been made in this important 



direction than is perhaps generally realized. Within the past year 



Schreiner and Shorey and their associates of the Bureau of Soils 



have reported in Bulletin No. 74 the isolation and study of over 



77543°— No. 3—11 2 



