Sodium Uptake by the Crayfish

Abstract

IT is now well established that many freshwater animals can absorb sodium and chloride ions from very dilute solutions. This was first demonstrated by Krogh¹ in animals which had been previously depleted of salt ; since then, it has been shown by the use of radioactive tracers that in the axolotl², in the frog³ and in the crab, Eriocheir ⁴, ion absorption occurs continuously in the normal animal as part of the mechanism for the maintenance of salt balance. Salt balance results when the rate of salt uptake equals the total loss of salt through the integument and by way of the excretory fluid, but little is known of the extent to which the uptake rate is regulated by the animal or of the internal or external factors upon which the uptake rate normally depends.