SYNCHRONISED GROWTH IN TETRAHYMENA CELLS 



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 Figure 2. The solid-line curve represents cell counts; the broken curve repre- 

 sents volume of cells per unit volume of culture. Standard procedure. (From 

 Zeuthen and Scherbaum, 1954.) 



Zeuthen, 1958). Furthermore, the division maxima build up (Figure 

 4 ) with fewer shocks— therefore in shorter time— the richer the medium 

 is. Medium A is 2 per cent proteose peptone; medium B is further en- 

 riched with 0.1 per cent, and medium C with 0.4 per cent, liver fraction 

 L. In all cases the synchronization is in 150-ml. shaker-flasks, and the 

 division indices are visually estimated on live samples removed from 

 the flasks. In this case periods of 20 minutes at 34° C. alternate with 

 40 minutes at 28° C. 



With continued temperature cycling, the synchronous system tends 

 to break down again. This, too, occurs fastest on the richest medium. 

 The eflPects shown in Figure 4 are paralleled by those of Figure 5, 

 which shows the times between the last temperature shock (E.H. := 

 end of heat) and the first division maximum, between the first and the 

 second, and between the second and the third maximum, all as func- 

 tions of the number of the temperature shocks. Both figures exhibit 

 broad optimal ranges for the number of shocks that must be applied to 

 give best synchrony. These ranges are shifted slightly towards fewer 

 shocks when the medium is rich. Under the best conditions it is seen 

 more clearly than from Figures 4 and 5 that the richer media give rise 



