SYNCHRONIZED GROWTH IN TETRAHYMENA CELLS 147 



the observed division synchrony. Some of Thormar's evidence (1959) 

 suggests that high activation energies are or may be involved in the 

 damage by heat. The following more general considerations are com- 

 patible with, and almost invited by, the observations presented. It is 

 clear that whenever we change the temperatvire in a growing biological 

 system, the rates of a great number of chemical reactions change. Each 

 reaction has its own temperature increment. The relative concentra- 

 tions of a great number of low-molecular intermediaries must change, 

 and the relative rates of formation of various more permanent macro- 

 molecular products may change. It is only because the biological sys- 

 tem is capable of a great deal of counterregulation that the Tetra- 

 hymena cell remains Tetrahymena at all temperatures from almost zero 

 up to 33 or 34° C— the upper limit for viability in our strain. That this 

 counter-regulation, or adaptation, is incomplete at the highest tempera- 

 tures is apparent from some of the information already given ( Figure 

 8 ) . That it is never complete is suggested by the observations, also by 

 Thormar (1956), listed in Table I. In the whole biotic range the size 

 of the cells is a function of the growth temperature, in this as in many 

 other organisms. This suggests that a balance between two metabolic 

 patterns (Hamburger and Zeuthen, 1957; Thormar, 1961), of which the 

 one supports general growth, the other division, depends on the tem- 

 perature. At the optimum temperature for population growth (28-29° 

 C. ) it is shifted maximally toward division. At this temperature there is 

 less growth between divisions than at any other temperature. Above 

 33° C. and at low temperatures the balance is shifted far to the oppo- 

 site side: at 34.1° C, say, preparation for division is never successful. 

 Holz, Scherbaum, and Williams ( 1957 ) synchronized the thermo- 



TABLE I 



Relative Volumes of Tetrahymena pyriformis Grown for Five Generations 

 at the Temperatures Indicated. Fixation Just Prior to Division. 



(Thormar, 1956). 



Temperature 



(centigrade) Volume 



32.0 152 



29.2 109 

 26.4 100 

 22.7 98 



19.3 110 



15.4 118 

 10.6 132 



