374 



PRINCIPLES OF SOIL MICROBIOLOGY 



curve, suggested by Robertson. 10 A difference exists in the physio- 

 logical activities and in the physico-chemical condition of young and 

 mature cells. 11 A medium, in which growth of a certain organism has 

 ceased as a result of accumulation of an injurious substance, may be 

 treated so as to neutralize the accumulated acid or alkali, the limiting 

 nutrient may be added, or finally the toxic substance may be destroyed 

 by means of heat. 12 The organism will then begin to grow again and 



24 48 72 96 120 



Time in hours 



Fig. 12. Rate of increase in numbers of a protozoan (after Cutler and Crump) 



pass through another cycle of activities. Limitations of growth and 

 formation of certain substances (ammonia, nitrate) may thus be due 



10 Robertson, T. B. On the nature of the autocatalyst of growth. Arch. Entw. 

 Mech., 37: 497-508. 1913; Tables for the computation of curves of auto- 

 catalysis, with especial reference to curves of growth. Univ. Cal. Publ. Physi- 

 ology, 4: 211-228. 1915. 



11 Sherman, J. M., and Albus, W. B. Physiological youth of bacteria. Jour. 

 Bact., 8: 127-138. 1923. 



12 Rahn, O. Uber den Einflusz der Stoffwechselprodukte auf das Wachstum 

 der Bakterien. Centrbl. Bakt. II, 16: 417-429, 609-617. 1906. 



