The mobilization of calcium and bicarbonate by raised concentrations of potassium in the haemolymph of the snail, Helix pomatia.

1. After the concentration of potassium in the haemolymph of Helix pomatia has been raised by the infusion of KCl, it falls approximately exponentially for a time and then tends to rise. The accompanying rise and fall of calcium concentration can be fitted to a simple mathematical model. 2. The mobilization of calcium is accompanied by the generation of bicarbonate in equivalent amounts, without much change in pH or Pco2. 3. There is probably an increased production or retention of carbon dioxide at this time, but the main cause of the changes in calcium and bicarbonate is not respiratory acidosis. 4. The concentration of potassium rises in snalis that have been infused with CaCl2. 5. The adverse responses visible in snails infused with KCl are largely prevented when CaCl2 is infused at the same time. 6. Homeostasis seems to involve the maintenance of a proper balance of calcium and potassium concentrations.