376 



PRINCIPLES OF SOIL MICROBIOLOGY 



in which A is the initial quantity of material subject to transformation, 

 x is the amount transformed in time t, and K is a constant. On in- 

 tegration, the equation becomes 



lo g ^- x = K { t-U) 



in which t\ is the time at which the reaction has proceeded half way to 



A 

 equilibrium, that is when x = — and K = kA. 



A 



Similar results have been obtained 16 for ammonia formation from 

 peptone by A. niger and for C0 2 evolution by fungi in the decomposition 



20 40 SO 80 100 120 140 160 130 200 220 240 260 280 300 320 i40 360 300 400 

 TIME IN H0UR5 



Fig. 14. Rate of CO* production from xylose by two fungi (after Peterson, 

 Fred and Schmidt). 



of pentoses. The formation by the microbial cell of toxic substances 

 which are selectively adsorbed on its surface has been demonstrated 

 by Rideal. 17 



The different microorganisms are not growing in the soil in pure 

 culture. In the presence of a great number of various other organisms, 



16 Waksman, S. A. Studies on proteolytic activities of soil microorganisms, 

 with special reference to fungi. Jour. Bact., 3: 475-492. 1918. 



17 Rideal, E. K. Colloid phenomena in bacteriology. Brit. Assn. Adv. Sci. 

 1923, 31-38. 



