438 M. H. JACOBS 



in these, as well as in other experiments, has shown itself to be 

 remarkably resistant to high temperatures as compared with the 

 ordinary races. In the second place, the temperature coeffi- 

 cient, Qi, in a given set of experiments is subject to far more 

 variation than in the case of starfish larvae, being as a rule much 

 higher (usually approximately 3) in the region above 40° than in 

 that below this temperature, and being subject at all times to 

 considerable and sometimes inexplicable fluctuations. For this 

 reason, calculations made by the method described are not so 

 exact as in the case of the starfish larvae, but fortunately this is 

 not necessary since Paramecium shows such a high degree of 

 acclimatization that the error due to the simplifying assumption 

 that the value, Qi = 3, applies to all temperatures is not able to 

 disguise this fact. In other words, the error that arises from 

 taking this value of Qi for the entire range, while, as a matter 

 of fact, it is considerably less at lower temperatures, is of such 

 a nature as simply to make the difference between the calculated 

 and observed death points less striking than it would otherwise 

 have been. If acclimatization is shown when such a simplifying 

 assumption is made, it would a fortiori be indicated if more 

 exact calculations had been made. 



This point will be made clearer by an actual example. It was 

 found in one set of experiments that for the three-vacuoled race, 

 Qi between 40° and 43° was equal to almost exactly 3.0. The 

 length of life after a sudden exposure to 41° was found to be 4.5 

 minutes, i.e., lo (taking this temperature as the standard of 

 comparison) was equal to 0.22. It was also found that when 

 the animals were heated gradually, at the rate of 1° in eight 

 minutes, the observed death point was very close to 44°. The 

 calculated death point, on the assumption that Qi is equal to 3.0 

 for all temperatures is approximately 40.6°, a difference of 3.4°, 

 indicating a very considerable amount of acclimatization. If 

 instead of assuming that below 40° the injury at any temperature 

 in unit time is only one-third as great as that at the temperature 

 one degree higher (as implied by the value, Qi =3), we had taken 

 into account the lower values of the temperature coefficient 

 which usually apply to this region, it is clear that the amount of 



