ADAPTATION OF FISH TO TEMPERATURE 553 
within two minutes, the rest were dead forty minutes later. The 
fish that had been immunized before were, with the exception of 
two individuals, all alive and normal after five hours. Yet, the 
tact that two of the fish succumbed may be an indication that their 
resistance to 35° was less than immediately after immunization. 
It is quite possible, however, that these two fish which had been 
kept in small dishes for such a long time had suffered through 
this captivity. 
This idea is supported by the fact that in a third experiment 
fish had kept their immunity to high temperature for thirty-three 
days after immunization against 35°. The immunization con- 
sisted in exposing the fish for three and six days respectively to 
27°. After that they were kept in the cold room for thirty-three 
days. When after that time subjected to a temperature of 35° 
they remained perfectly normal for five and a half hours, when the 
experiment was discontinued. 
We made a large number of experiments in which the duration 
of the immunity against high temperatures was tested sooner after 
the process of immunization than in the above mentioned experi- 
ments. In all these experiments it was found that the fish did 
not lose their immunity against temperatures of 39° and 35° 
respectively if they were put into the cold room for a period of 
thirty-three days or less after immunization. 
VI. EXPERIMENTS WITH FISH KEPT AT A CONSTANT 
TEMPERATURE OF 0°4 C. 
The fish which we used for this experiment were caught in 
January and kept since that time in a cold room in which the 
temperature varied between 10° and 14°C. Our experiments 
showed that these fish died in a rather short time when suddenly 
put into a diluted Ringer solution or diluted sea-water of 31°, 
provided that the concentration of the solution was below m/8. 
In an m/8 or m/4 Ringer solution or sea-water they were able to 
resist the temperature of 31° without any previous immunization. 
We put a large number of these fish in an icé chest in which the 
temperature remained constantly at 0.°4, and investigated at 
various intervals whether the resistance of these animals to a 
