Physiology 483 



temperature in Amoeba proteus, so that binucleate forms are occasionally 

 seen toward the limits of the range (86). Freezing (111, 239, 576) and 

 prolonged exposure to sub-zero temperatures (111) are fatal to active 

 stages of many species, although cysts of Colpoda have survived exposure 

 to liquid air (546). 



Little is known about biothermal ranges of individual species. How- 

 ever, fission occurs in Amoeba proteus at 11-30° (86); in Astasia longa at 

 15-30° in peptone media and at 22-30° in ammonium-N media (506); and 

 in Chilomonas Paramecium between 9.5 and 35° (529). An optimum for 

 fission has been reported in a few species: Paramecium aurelia, 24-28.5° 

 (581); Chilomonas Paramecium, 26-30.5° (531); Astasia longa, 30° (506); 

 Tetrahymena geleii, 28.5° in the range, 7.8-28.5° (441). Euglena gracilis, 

 in peptone medimn, has shown an optimum of 10° in darkness. With sup- 

 plementary acetate, the optimum is shifted to about 23° which is approxi- 

 mately that for growth in light (243). 



Temperature coefficients (Qio values) and thermal increments ([x val- 

 ues) for fission have been calculated in several cases. For Paramecium 

 aurelia, Qio = 2.7 at 21.5-31.5° (581); for P. aurelia, [j. = 23,000 calories at 

 12-25° (400); for fission of Amoeba proteus (86), ^ — 16,500 calories at 

 11-30°, and for cytoplasmic division [x = 20,500 (11-21°) and 7,300 (21- 

 30°). For Tetrahymena pyrijormis, Q,,, and jj, values vary with the 

 temperature range: at 7.8-12.3°, Qu. = 9.7 and [x = 35,800 cal.; at 12.3-20°, 

 Qto = 3.0 and jl = 18,400; at 20-28.5°, Qio = 1-5 and ^ =7,350 (441). 

 Reported Q^o values (22-28°) for Astasia longa vary with the medium — 

 2.10 in peptone, 2.17 in acetate and peptone, 1.28 in acetate and ammo- 

 nium-N, and 8.03 in an inorganic medium (506). 



The use of thermal coefficients and thermal increments in biology 

 has been based upon the assumption that Q^o and [i values are related 

 to the nature of a reaction, and upon the hope that a study of such 

 data might furnish clues to the fundamental nature of various biological 

 phenomena. The Q^,, value is the coefficient of increase in the velocity of 

 a reaction for each 10° increase in temperature. Qio values are calculated 

 from the equation, 



, ^ 10 (log ki - log k2) 



log Q,o = — ^ ^/ ^ ^ ^ 



tl — to 



in which k^ represents the reaction velocity at temperature t^ and ko the 

 velocity at temperature to. Log k is a linear function of temperature 

 (Centigrade). For a particular reaction, Q^o values vary with temperature 

 and usually increase as the temperature decreases. For example, Qio 

 may be 10 or greater for a given reaction at low temperatures, as com- 

 pared with 2 or less for a higher range. 



The thermal increment, described by the law of Arrhenius, is calculated 

 from the equation. 



