UPPER THERMAL DEATH POINTS 429 



injuiy before the final temperature had been attained. The 

 possibihty exists, however, on the other hand, that the slower 

 rate would be more favorable than the rapid one in giving greater 

 opportunity for adjustment or acclimatization to occur. Which 

 of these two alternatives is the correct one for a given form can, 

 , as a matter of fact, be decided only by experiment. 



In the present paper a method is suggested for determining 

 this point and for dealing quantitatively with certain other 

 aspects of the general problem of acclimatization. The writer 

 wishes to express his indebtedness to Prof. F. R. Lillie for kindly 

 placing at his disposal on several occasions the facilities of the 

 Marine Biological Laboratory at Woods Hole and to Mr. Francis 

 H. Adler for assistance in making certain of the observations on 

 which the paper is based. 



2. MATERIAL AND APPARATUS 



In the experiments to be described, the use of both methods 1 

 and 2 was necessary for the quantitative estimation of the extent 

 to which acclimatization occurs. For this reason, only small 

 organisms were employed, starfish larvae eighteen to forty-eight 

 hours old and Paramecium caudatum being the ones chosen. 

 The medium in which they were heated was for the starfish 

 larvae fresh sea-water and for Paramecium, in most cases, the 

 natural culture fluid filtered to remove all animals. It was 

 recognized that the complex nature of the culture fluid might 

 introduce undesirable complicating factors, but preliminary 

 experiments showed that, as a matter of fact, distilled water, 

 w^hich would naturally have been preferred on account of its 

 uniform composition and in which the animals lived normally 

 at room temperature for days, was quite tinsuitable for sudden 

 exposures to high temperatures, the animals dying far more quickly 

 in it than in their own culture medium, and the results obtained 

 being markedly irregular. That at least part of the effect of the 

 distilled water was of an osmotic nature was shown by the fact 

 that the addition to the same water of slight amounts of neutral 

 salts or even of cane sugar made it considerably less injurious. It 



THE JOURNAL OF EXPERIMENTAL ZOOLOGY, VOL. 27, NO. 3 



