STIMULATING EFFECTS OF CROWDING 169 



only when more than one Hving cell is present and that the presence 

 of a second cell which has died does not affect it. He particularly 

 criticizes the work of Cutler and Crump and of Peskett because of 

 the high death-rate in their subcultures, not only among the inocu- 

 lum but also, as Cutler and Crump have shown, among the animals 

 produced in the subculture itself. He also criticizes the artificial me- 

 dium used by the latter investigators, and presents evidence to show 

 that their synthetic medium is not well buffered above pH 7.8, which 

 is the optimum region for the growth of Enchelys. Data are also 

 presented showing the great difference in viability of different In- 

 fusoria from a crowded culture, and he suggests that a part of the 

 discrepancy between his own work and that of Cutler and Crump is 

 due to differences in the protozoan-bacteria ratio on account of the 

 different techniques employed. 



Greenleaf (1926) reported in full his experiments along this line, 

 using Paramecium aurelia, P. caudatum, and Pleurotricha lanceolata, 

 inoculated in from 2 to 40 drops and Stylonychia pustiilata in 2 and 

 5 drops of culture medium, to determine the influence of volume of 

 culture medium on the rate of cell division, and the influence of cell 

 proximity on this rate, and to investigate the factors concerned with 

 the lag period. In the experiments covering the first point, Greenleaf 

 reports the results by means of giving the average per diem rate car- 

 ried through a period of 5 days. Under these conditions, in 4 experi- 

 ments only, out of 27, were 2 drops found to be more favorable for 

 reproduction than 5 drops. Similarly, in only 4 experiments out of 

 27, did the 5-drop cultures give a higher rate of reproduction than 

 the 20-drop cultures. In the comparisons between the 20- and the 

 40-drop cultures, the former gave a higher rate in 8 experiments; the 

 latter in 9 cases; and i was a tie. 



Again, in his investigation of the effect of 2 animals present in a 

 given volume, 2 or 5 drops, he used the average per diem division 

 rate based on 5-day periods and found that the single animals divid- 

 ed the more frequently in both cases, although he did find that 

 "there was less difference in the division rates of the animal carried 

 alone and the two carried together in the 5-drop series than in the 

 2-drop series. This indicates that in the larger volume the depressing 



