ABSTRACT
There was no change in the body volume of marine Peritricha subjected to reductions in the salt concentration of the medium, so long as the osmotic pressure of the medium was kept constant by the addition of urea, glycerol, or cane-sugar. In mixtures of isotonic non-electrolytes with sea water the rate of vacuolar output was decreased—more so in the case of urea than of glycerol. It is concluded that the cell membrane is relatively impermeable to urea, glycerol, and cane-sugar, and also to neutral salts.
Excretory substances could not be produced in sufficient quantity to attract water into the contractile vacuole by osmosis at the rate observed. The process of diastole therefore involves “secretion” of water by the vacuolar walls.
Cyanide and sulphide in very low concentrations rapidly caused a great reduction in the rate of output of the contractile vacuole of marine Peritricha. In the case of cyanide this effect was rapidly reversible. Alcohols and urethane only decreased the rate of vacuolar output when present in much higher concentrations. It is suggested that possibly vacuolar activity depends directly on an oxidative process.
When marine Peritricha were transferred from dilute sea water to dilute sea water of the same concentration + cyanide M/200 or M//500 (the />H being carefully controlled), the contractile vacuole was completely or almost completely stopped, and the body increased in volume. When the organism was transferred back to dilute sea water of the same concentration without cyanide, the contractile vacuole became active again and the body decreased in volume until a new steady value was attained which was rather below the value in dilute sea water before cyanide treatment.
The increase in body volume consequent on treatment with cyanide was greater the more dilute was the sea water. For sea water of concentrations of 100-75 Per cent, no swelling was detectable when the organism was treated with cyanide.
The rate of output of the contractile vacuole is sufficiently great to account for the decrease in body volume during recovery from cyanide.
The permeability of the body surface to water is estimated as o-o5-O’io cubic miera per square micron per atmosphere per minute.
I.e. the body weight when in 100 per cent. sea water, and assuming a specific gravity of 1.1, which is probably a little too high.
