710 PRINCIPLES OF SOIL MICROBIOLOGY 



cal condition of the soil, consisting of a knowledge of the qualitative 

 and quantitative composition of its microflora and microfauna, can be 

 considered as an expression of its complex chemical and physical 

 condition. 



Chester 4 was the first to suggest a formula for determining the coeffi- 

 cient of "zymotic efficiency/' which would express the results of a 

 quantitative-qualitative bacteriological analysis of soil. "Zymotic 

 efficiency" was looked upon as a compound involving a number of 

 factors, capable of individual expression. Large numbers of bacteria 

 combined with great activity would show a high zymotic efficiency, 

 while low efficiency would mean small numbers and low activity. The 

 lack of proper bacteriological methods, combined with an insufficient 

 knowledge of the various groups of soil organisms prevented Chester 

 and those following soon after from developing this idea. 



Following the work of Chester, the study of soil microbiological 

 activities was divided along two main lines: (1) an intensive study of 

 numbers and types of microorganisms occurring in the soil, and (2) a 

 study of the chemical changes taking place when a small amount of 

 soil is added to sterile or unsterile solutions of definite composition, or 

 when a definite chemical substance is added to a definite amount of 

 soil and the transformations taking place are determined, after a definite 

 period of incubation. 5 The principle of the original solution method 

 consisted in inoculating various solutions, the composition of which 

 depended upon the transformation under consideration, with compara- 

 tively large amounts of soil and determining, at the end of a definite 

 period of incubation, the chemical change that has taken place. When 

 a 1 per cent peptone solution is inoculated with ten per cent of soil, 

 and the ammonia formed determined after 4 to 8 days incubation at 

 20°C, a correlation could be demonstrated between the amount of 

 ammonia thus formed and the productivity of certain soils. Lohnis 

 laid down two considerations which could be observed in carrying on 

 these experiments: 



1. The course of various transformations should be demonstrated quantita- 

 tively. 2. The composition of the soil solutions should be of such a nature that 



4 Chester, F. D. Study of the predominating bacteria in a soil sample. Del. 

 Agr. Exp. Sta. Rpt., 14: 52-66. 1903; Bui. 65. 1904. 



6 Remy, Th. Bodenbakteriologische Studien. Centrbl. Bakt. II, 8:657, 

 699, 728, 761. 1902; Landw. Jahrb. Erganzb., 4: 31. 1906; Ehrenberg, P. Die 

 bakterielle Bodenuntersuchung in ihrer Bedeutung fur die Feststellung der 



