244 MICROBIOLOGY OF SOIL. 



suggested the use of special media for the quantitative estimation of 

 different physiological reactions; thus, making a i per cent solution of 

 peptone, and inoculating with equivalent quantities of soil, he caused the 

 decomposition of the peptone and the formation of ammonia, and secured 

 comparisons of the ammonifying power of different soils. In a similar 

 manner he used special solutions for comparing quantitatively the trans- 

 formation accomplished by nitrifying, denitrifying or nitrogen-fixing 

 bacteria. 



Remy's method has been extensively tested by Lohnis, Ehrenberg, 

 Lipman and others. It has been shown to possess a serious defect in 

 that it deals with conditions unlike those occurring in the soil itself. For 

 this reason more recent investigations have been carried on in weighed 

 portions of soil rather than in culture solutions inoculated with 10 per 

 cent of soil as is done in Remy's method. 



RATE OF OXIDATION OF CARBON. The rate of decomposition of 

 humus or of other organic matter in the soil may be measured, as was 

 done by Wollny, by determining the amount of carbon dioxide evolved 

 in weighed quantities of material kept under definite conditions. The 

 influence of temperature, moisture, aeration, organic matter, antiseptics, 

 etc., has been determined in this manner. The same rrfethod may be 

 used in studying decay, and factors influencing decay, in soils m situ 

 that is, in the field. 



More recently Russell and his associates have modified the method 

 in that they have determined the rate of oxidation of carbon not by 

 measuring the carbon dioxide evolved, but by estimating the amount of 

 oxygen absorbed. In either case decay is measured from the carbon 

 standpoint. The method based on this principle should find wide 

 application in future soil fertility investigations. 



RATE OF OXIDATION OF NITROGEN. Another method or series of 

 methods for studying decomposition processes in the soil may be based 

 on the determination of nitrogen compounds formed in the breaking 

 down of proteins. Two of the derivatives of protein, namely, ammonia 

 and nitrate, have been used successfully to gauge the decomposition of 

 organic matter in the soil. The recent results secured by Lipman and 

 his associates demonstrate that ammonia formation from dried blood in 

 weighed quantities of soil may serve as a very accurate measure of decay 

 from the nitrogen standpoint. Corresponding determination of nitrates 

 may similarly be employed in tracing protein cleavage and trans- 



