UPPER THERMAL DEATH POINTS 



437 



shown to hold in this region. It may also be noticed that for the 

 region from 32° to the point of death in these particular experi- 

 ments the value of Qi is in general higher than 2.0, the approx- 

 imate average value for the whole range of temperature studied. 

 In the last column of table 3, the theoretical death temperature 

 is therefore calculated for comparison from the value, Qi=2.2. 

 It will be noticed that in either case the calculated death tem- 

 perature lies within a few tenths of a degree of that actually- 

 observed, and the amount of acclimatization that has occurred, 

 if any, is consequently extremely small. In similar experiments 

 on Paramecium, immediately to be described, the difference may 

 amount to several degrees. 



5. EXPERIMENTS ON PARAMECIUM CAUDATUM 



In the case of Paramecium, the results are more complicated. 

 In the first place, there is considerably more cultural and racial 

 variation in the length of life at any given temperature (de- 

 termined by method 1) than in the case of starfish larvae w^here 

 the results, on the whole, seem to be remarkably uniform. This 

 is show^n in table 4 where some of the results obtained with this 

 form are summarized. 



The figures in columns 6 and 7 and probably in column 1 are 

 for the three-vacuoled race described by Hance ('15, '17), which 



TABLE 4 



Times required to kill approximately one-half of the individuals of Paramecium 

 caudaium of different races at different temperatures 



