1. The rate of pulsation of the anterior contractile vacuole of Paramecium caudatum under chloretone anesthesia has been determined over a range of temperatures from 9–31°C. It has been found that the rate is a logarithmic function of the temperature according to the Arrhenius equation. From 9–16° the temperature characteristic (µ) has the value 25,600; from 16–22° it is 18,900; and from 22–31° it becomes 8,600.

2. It is concluded that there are at least three underlying reactions responsible for pulsation, the rates of which vary. Which reaction becomes the limiting one depends upon the range of temperature considered.

3. It does not appear that oxidative processes alone determine the rate of pulsation, although they may be of fundamental importance.

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