536 GROWTH 



70,000 times gave no allelocatalysis (Phelps, 1935). Darby (1930) 

 maintained that allelocatalytic effects were due to the pH of the medium, 

 and Jahn (1933) beheved them due to the oxidation-reduction poising 

 of the medium. When the medium was optimum, there would be no 

 increased rate of reproduction; but if the medium was suboptimum, 

 two or more organisms might modify it enough to permit growth whereas 

 one organism could not do so and would grow slowly or fail to survive. 



Johnson and Hardin (1938) reported that medium conditioned by 

 the growth of Pseudomonas fluorescens inhibits the reproduction of 

 Varamecium micronucleatum. With the saline medium, used old-cul- 

 ture medium was as efficient as fresh medium. The difference between 

 these and Woodruff's conclusions may be due to the effects of mixed 

 bacteria in the natural medium used by Woodruff. Kidder (1939) stud- 

 ied the effect of conditioning with a bacteria-free Colpidium campylum 

 culture in proteose-peptone, dextrose broth. He believes that there is an 

 accelerator and an inhibitor in the conditioned medium for growth. 

 These were separated by absorption and filtration. Caution should be 

 exercised in the use of filtered media, as some kinds of filters make the 

 filtrate toxic (Richards, 1933). 



Sweet (1939) reinvestigated the volume seeding relation, using Eu- 

 glena gracilis, and found that seedings of one and two individuals grew 

 better in four drops of about 0.05 ml. each and inoculations of four and 

 eight individuals in slightly larger, five-drop environments. This au- 

 thor's methods and technique illustrate survival, rather than growth, 

 and while a volume effect of the environment was found, her results 

 did not support the Robertson theories. 



The observations of these investigators and others focused attention 

 on the suitability of the culture medium and suggested that the allelo- 

 catalytic effects found by some biologists and discredited by others might 

 be explained on this basis. Woodruff's (1911) demonstration that the 

 waste products limited growth was recalled and clarified some of the 

 volume effects on growth, wherein the yield of cells depended on the 

 volume of the culture medium rather than on the size of the inocula- 

 tion. Johnson (1933) explained allelocatalytic effects on the relation 

 of the bacterial food concentration to the number of Protozoa in the 

 culture. An allelocatalytic effect on P. caudatnm and on Moina macro- 

 copa was found with a high nutrient concentration, and the reverse of 



