ADAPTATION OF FISH TO TEMPERATURE 551 
IV. THE SUMMATION OF THE IMMUNIZING EFFECTS OF SHORT 
PERIODS OF EXPOSURE TO HIGH TEMPERATURE 
In the immunization experiments described thus far the fish 
had been exposed continuously for a rather long period of time to a 
temperature of 27°. We wanted to know if it was possible to 
immunize them for a higher temperature by exposing them only 
a short period of time each day and keeping them in the interval 
at a temperature of from 10° to 14°C. This would mean that 
the immunizing effect produced in the animal during a short 
exposure to a high temperature would be preserved at least twenty- 
four hours until the next exposure to a high temperature took 
TABLE 8 
DATE | - DURATION AND TEMPERATURE OF EXPOSURE 
March 
a 1 hour from 17° to 31° 2 hours at 31° 
8 1 hour from 17° to 33° 2 hours at 33° 
9 1 hour from 18° to 35° 2 hours at 35° 
11 3 hours from 11° to 37° 
12 2 hours from 17° to 37° 
13 2 hours from 16° to 37° 
14 2 hours from 17° to 37° 
15 2 hours from 17° to 37° | 2 hours at 37° 
16 2 hours from 17° to 37° 2 hours at 37° 
18 | 2 hours from 17° to 38° 14 hours at 38° 
19 2 hours from 18° to 38° | 2 hours at 38° 
20 2 hours from 19° to 39° 2 hours at 39° 
place; and would be added to the immunizing effect of the next 
exposure to a high temperature. Table 8 gives the periods of 
exposure. 
Most of the fish died on the third day when the temperature 
was raised only to 35°. For this reason we did not dare to 
expose the fish for more than a few minutes to a temperature of 
37° on the 11th, 12th, 13th and 14th of March. The fish were ex- 
posed to a higher temperature for not more than four hours on 
one day. We have seen that an exposure of four hours in itself 
does not suffice to create immunity to a temperature of 35° or 
above. Hence the fact that these fish were finally able to resist a 
