Synchronous divisions in mass cultures of the ciliate proiozoon Tetrahymcna pyriformis 



second temperature rise should have come still earlier, and we then realized that it 

 would be much better if we did not let even the first peak develop. Instead we sup- 

 plied the stimulus for it by one short heat shock, but did not let it develop because the 

 culture was subjected to another shock before it could do so. Hoping to concentrate 



6 8/0/2 W 



/hoars 



Figure 5. Standard intermittent heat treatment produces 

 cycling in the culture after return to optimum or to room 

 temperature. In this as in other graphs the temperature 

 curve shows the switches of the control clock. In the 

 culture the temperature fluctuates with the amplitude 

 indicated, but more nearly according to a sine curve. 



H7 



