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

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Abstract
1. The effects of external and internal sodium concentrations on the uptake of sodium ions by the crayfish, Astacus pallipes, has been studied. 2. The normal sodium influx, measured with 24Na, from O.3 mM /l. NaCl solution is 1.5 µM./10 g. body weight/hr. The rate of loss of sodium to de-ionized water has roughly the same value. 3. Net loss of sodium reduces the external sodium concentration required for sodium balance. The minimum equilibrium concentration is about 0.04 mM./l. NaCl. 4. The relation between the external sodium concentration and the sodium influx is non-linear. The influx has a maximum of about 10 µM./10 g./hr. at an external concentration of approx. 1 mM./l. 5. The 24Na influx is a true measure of the sodium uptake rate at low external concentrations. At higher concentrations the influx may exceed the uptake rate by some 20%. 6. Net loss of sodium increases the influx by three to five times. Loss of 5-10% of the total internal sodium increases the influx from the normal to the maximum level. A 1% change has a significant effect on the influx. Changes in the internal sodium content reflect changes of the blood sodium concentration. 7. A scheme is suggested whereby the external and internal sodium concentrations interact together on the influx to produce a self-regulating system which maintains the animal in sodium balance.