1. The rate of output of the contractile vacuole in a fresh-water peritrich ciliate (Carchesium aselli) varies with temperature with a Q10 of about 2·5-3·2, or a µ of about 17,000, over the range 0-30° C.

2. There is a slow decline in output during exposure for several hours to high temperatures (25-30° C.). At still higher temperatures (34° C.) a high rate of output is maintained for a few minutes, but swelling and death rapidly ensue.

3. The frequency of uptake of food vacuoles also varies with temperature, increasing from 0 to about 24° C., but decreasing at higher temperatures. At about 0° C. and at temperatures above about 30° C. no food vacuoles are taken up and the adoral cilia remain extended and motionless.

4. No change in body volume could be detected during exposure to high temperatures (25-30° C.) for two or more hours, even though the rate of vacuolar output was increased to three or four times its normal level at 15° C. It is concluded that the rate of uptake of water from the outside medium must have been increased correspondingly.

5. It is suggested that temperature affects the permeability of the organism to water, and that the rate of vacuolar output is adjusted accordingly, although on the evidence so far presented other explanations are possible.

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