The Physiology of Contractile Vacuoles

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Abstract
1. Evidence from osmotic experiments indicates that the amount of osmotically inactive material in the suctorian Podophrya is small, and that the internal osmotic pressure of the cytoplasm is approximately that of a 0-04 M solution of non-electrolyte. 2. When the internal osmotic pressure of Podophrya is raised to an abnormally high level by equilibration with a solution of ethylene glycol or with dilute sea water, and the organism is then transferred to tap water, the rate of vacuolar output is temporarily raised far above its normal value. The body swells only slightly. This is taken as good evidence for osmoregulation. 3. When Podophrya is placed in a dilute solution of sucrose the rate of vacuolar output (relative to the original rate in tap water) decreases rectilinearly with the concentration of sucrose used, reaching zero at about 0.04M. This is as would be required for good osmoregulation. 4. There is a slight lag in the response of the contractile vacuole to a change of medium. It is suggested that this delay in adjustment of the osmoregulatory mechanism must result in a slight change of body volume, which could be the basis for the control of vacuolar output.

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