General Trends 339 



(Mganisins, as b\ proper aeration and provision of sufficient moisture, 

 nimierous reactions immediately take place. These are accompanied 

 1)\- a rapid rise in temperature, which may serve as a measure of the 

 rapidity of the decomposition process. The microbiological popula- 

 tion of the compost changes with a change in temperature and with 

 the nature of the materials undergoing decomposition. Among the 

 major chemical reactions that take place during the process of com- 

 posting, the destruction of the cellulose and hemicelluloses, and the 

 resulting increases in ash, lignin, and protein contents are most sig- 

 nificant. Protein synthesis is brought about by the activities of the 

 microorganisms. 



One of the major economic problems involved in the preservation 

 of stable manures is the potential loss of nitrogen, as pointed out 

 previously. Various methods have been utilized for the conservation 

 of the manure, the major purpose being the prevention of these losses. 

 One of these methods consists in hastening the activities of micro- 

 organisms which bring about the destruction of the cellulose and 

 hemicelluloses in the manure; if the microbiological population is 

 sufficiently active to bring this about during the early stages of com- 

 posting, the soluble forms of nitrogen in the manure will be rapidly 

 transformed into complex insoluble organic forms. 



The survival in the soil of organisms causing plant and animal 

 diseases has also received considerable attention. Among the plant 

 diseases, the root rots, take-all diseases of cereals, soft rots, scabs, 

 club roots, and numerous others brought about by fungi, actinomy- 

 cetes, and bacteria are particularly important. To these should be 

 added the many insect pests which pass a part of their life cycle in 

 the soil, and the various diseases caused by worms and other animal 

 forms. Numerous methods of control have been developed, ranging 

 from partial sterilization by heat and chemicals to the introduction 

 of bacteria, fungi, and nematodes destructive to the parasite. 



The fate of bacteria causing epidemics of animal diseases, and that 

 of fungi and actinomycetes causing less widespread outbreaks of 

 skin diseases and deep-seated diseases, have received considerable 

 attention. The study of antagonistic organisms found in the soil 

 and their formation of substances destructive to the pathogens is now 

 making rapid progress. 



Recent trends in soil microbiology have thus centered upon a 

 better understanding of the nature and complexity of the soil popula- 

 tion, the conditions which influence its quantitative and qualitative 

 composition, the activities of these organisms in the soil, and the 



