The Physiology of Contractile Vacuoles

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Abstract
1. The rate of output of fluid from the contractile vacuole of a fresh-water Peritrich Ciliate was decreased to a new steady value immediately the organism was placed in a mixture of tap water and sea water. The rate of output returned to its original value immediately the organism was replaced in tap water. The contractile vacuole was stopped when the organism was treated with a mixture containing more than 12 per cent, of sea water. 2. Transference of various species of marine Peritricha from 100 per cent, sea water to mixtures of sea water and tap water led to an immediate increase of the body volume to a new and generally steady value. Return of the organism to 100 per cent, sea water led to an immediate decrease of the body volume to its original value or less. 3. Marine Peritricha showed little change in rate of output when treated with concentrations of sea water between 100 and 75 per cent. In more dilute mixtures the rate of output was immediately increased, and then generally fell off slightly to a new steady value which was still considerably above the original (100 per cent. sea water) value. The maximum sustained increase was approximately x 80. Return of the organism to 100 per cent, sea water led to an immediate return of the rate of output to approximately its original value. 4. When individuals of some marine species were placed in very dilute concentrations of sea water, the pellicle was frequently raised up in blisters by the formation of drops of fluid underneath it, and the contractile vacuole stopped. 5. Evidence is brought forward to suggest that in the lower concentrations of sea water marine forms lost salts. 6. The contractile vacuole probably acts as an osmotic controller in fresh-water Protozoa. Its function in those marine Protozoa in which it occurs remains obscure.

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