CROWDING AND INCREASED DEATH-RATE 



137 



events is shown in Figure 9, which is taken from the work of Myers 

 with Paramecia. 



If the initial volume is relatively large (16 drops, or about 0.8 ml.), 

 Myers finds that fission begins at about the same rate, so far as 1 2- 

 hour periods of observation show, regardless of whether the seeding 

 be with I, 2, or 4 individuals. The population of such cultures rises 

 rapidly to a peak which is essentially the same for all the seedings 

 just mentioned; at its peak it ranges from 123 to 126 individuals and 



It 



IB 



Fig. 9. — Showing the rise and decline of populations of Paramecia in 0.8 cc. of 

 culture fluid by, respectively, i, 2, 4, and 8 individuals. The horizontal axis shows 

 successive periods of 12 hours each; the vertical axis gives numbers of individuals in 

 the populations. (From Myers, 1927.) 



then falls off at about the same rate. The cultures seeded with a 

 single individual take longer to reach the maximum than do those 

 seeded with 2 or 4, but otherwise the course of the population history 

 is similar. 



When 8 individuals are introduced in place of i, 2, or 4, the maxi- 

 mum in Myers' cultures showed a population of only half that given 

 with the smaller seedings. The reason for this difference is not clear. 

 On the surface it appears that the larger initial seeding either ex- 

 hausts the food supply more speedily or poisons the culture medium 



