506 JACQUES LOEB AND HARDOLPH WASTENEYS 
The following idea for the explanation of the mechanism of 
adaptation suggests itself. The rise in temperature brings about 
certain changes especially in the surface of the cells or the body 
of the animal, whereby the latter loses its protective impermea- 
bility. If the rise in temperature occurs gradually the blood 
(and especially the salts of the blood or of the surrounding solu- 
tion or of both) has time to repair the damage. If the rise, how- 
ever, occurs suddenly then the damage done cannot be repaired 
‘quickly enough by the blood, or the salts of the surrounding solu- 
tion, to prevent the death of the cell or the animal. The peculiar 
influence of the concentration and nature of the surrounding solu- 
tion described in this paper would harmonize with this suggestion. 
A second possible suggestion is that under the influence of the 
higher temperature a substance is formed in the animal which 
protects it against the effects of high temperature. The formation 
of this substance is also a function of time and for this reason an 
animal can keep alive if the temperature is increased gradually 
but cannot keep alive if it is increased rapidly. 
Both suggestions would explain the fact that if an animal is 
once immunized against a high temperature it will keep this im- 
munization, for some time at least, even if kept at a low tempera- 
ture or on ice. Further experiments with which we are occupied 
may decide between these and other possible suggestions. 
SUMMARY 
1. Experiments were made with Fundulus which were caught 
in the winter and kept at a low temperature (from 10° to 14°C), 
to find out the maximum temperature into which they could, with 
impunity, be transferred suddenly. It was found that the maxi- 
mum temperature varied with the concentration of the sea-water 
or a Ringer solution; being about 25°C. for a concentration of 
m/128 or m/64; 27°C. for a concentration of m/32; 31°C. for a 
concentration of m/8, and almost 33°C. for a concentration of 
m/4. The latter concentration was the optimum, the resistance 
to high temperature decreasing again with a further rise in con- 
centration. 
