The Absorption of Chloride Ions by the Crayfish, Astacus Pallipes Lereboullet

1. The mechanism of chloride uptake in the crayfish, Astacus pallipes, has been investigated. 2. In the absence of chloride uptake, chloride is lost from the animal at a mean rate of 0.8 µM./hr./10 g. body weight. This is about 72% of the sodium loss rate. 3. In salt-depleted animals, chloride balance can be maintained at a minimum external concentration of 0.028 mM./l. This is lower than the corresponding value for sodium. 4. In salt-depleted animals, chloride is taken up from sodium chloride solutions above the equilibrium concentration, but at about one-third of the rate of sodium uptake. From potassium chloride solutions the net uptake of chloride is slight or non-existent. The addition of sodium increases the rate of net chloride uptake from KCl. 5. The chloride influx is always high and is similar from sodium and potassium chloride solutions. The influx is much higher than expected from measurements of loss rate and net uptake. Up to 90% of the influx may be accounted for by exchange diffusion. 6. Activation of the chloride uptake mechanism can be brought about if the animal is made deficient in chloride only. Chloride influx is not increased but the rate of net uptake may now be high and account for 70% of the influx. 7. Net uptake of chloride by chloride-deficient animals takes place against an electrochemical gradient and chloride is exchanged for other anions, probably bicarbonate.