STUDIES ON THE THERMAL DEATH OF HYALELLA AZTECA (SAUSSURE)

¹ Iowa State Teachers College and the Iowa Lakeside Laboratory

1. Thermal death occurs in Hyalella asteca at constant temperatures from 33° to 50° C. The time required to produce thermal death varies from more than eleven hours (39,600 seconds) at 33°, to less than one second at 50° C.

2. Comparison of Q₁₀ values for narrow ranges within the broad range of temperatures investigated indicates a marked decrease of Q₁₀ values at higher temperatures in spite of a more rapid lethal effect.

3. Thermal death occurred in rising temperatures, the slower the rate of rise, the lower the killing temperature, being not below 39° nor above 41° for the rates of rise investigated.

4. A temporary adjustment was found to occur to rising temperatures, delaying thermal death at a given temperature for some time past the period necessary to kill on immersion in the constant temperature bath at the given temperature.

5. Resistance to the effects of heat appears to be directly related to the size and age of the animal, the older and larger the animal the greater the resistance, except for the largest animals (which might have reached a state of senility).

6. Resistance to the effects of heat does not appear to be related to sex in Hyalella azteca.