550 GROWTH 



initial densities up to 70,000 times failed to show any allelocatalytic 

 effect. The number of animals present at the end of the logarithmic 

 phase was independent of the number in the seeding. In comparing 

 the phases of Glaucojua population growth with those of bacterial and 

 yeast populations, he found the following differences: the initial station- 

 ary and lag phases in Glaucoma populations are much shorter, in propor- 

 tion to the optimum generation time; the stationary phase is independent 

 of the size of the seeding; and the change from the logarithmic to the 

 equilibrium phase of growth is more abrupt. No period of decreasing 

 population size appeared within 120 hours. 



Changing from yeast extract to yeast autolysate increased the yield 

 (Phelps, 1936) . The rate of growth was found to be independent of the 

 food concentration within wide limits, but the total number of animals 

 was proportional to the amount of food. The concentration of excretion 

 products did not inhibit the growth until very great population densities 

 were reached. This again is quite different from yeast cells, which are 

 adversely effected by low amounts of excretion and fermentation prod- 

 ucts. A more favorable food medium and the use of aeration flasks, 

 as well as differences in the species of animals used, may account for 

 the lesser effect of waste products observed by Phelps than by Wood- 

 ruff (1911). The G. pyrijormJs used by Phelps is identified now as 

 Tetrahymena glaucomiforma. 



The growth of populations of Colpidium campylum was measured 

 by Bond (1933). With small amounts of yeast autolysate, the growth 

 was slight and the lag period was greatly prolonged. With greater 

 amounts of food, the equilibrium population was greater, the logarithmic 

 phase was longer, the rate of growth greater, and the transition from 

 the logarithmic phase to the equilibrium phase of the growth curve less 

 abrupt. Bond's evidence suggests that the yield of animals depends 

 more on the amount of food available than on an inhibitory effect of 

 excretion products. 



Gause (1934) presented the growth of a population of P. caudatum 

 on an oatmeal infusion, with bacteria. He fitted the S-shaped growth 

 curve with the logistic equation, and his analysis of the curve has been 

 mentioned before. The growth curve of Stylonychia pustulata, Fig. 134, 

 illustrates rapid growth, with a short equilibrium phase, followed by 

 a period of negative growth leading to a lower equilibrium level. The 



