ABSTRACT
Recent investigation has shown that the fully aquatic, larval form of the salamander Ambystoma tigrinum handles osmotic and ionic regulatory problems as do other fresh water and semiterrestrial animals. Faced with osmotic water entry from a hypotonic environment, it excretes a dilute urine to remain in water balance. Uptake of NaCl from artificial-pond water occurs at the rate of about 1μ-equiv. (10 g.)−1hr.−1. This maintains an ionic steady state by compensating for losses in the urine and by diffusion across the skin and gills (Alvarado, 1962; Alvarado & Kirschner, 1963). Animals in a steady state in pond water ([NaCl] = 1·2 mM/1.) have a potential difference across the body surface of 10–20 mV., body fluids positive to the external solution. Nothing is known about the mechanism generating electrical asymmetry in these animals.
A detailed study of the effects of salt depletion on fluxes of sodium and chloride has been under-taken by R. H. Alvarado. The results will be reported in another publication.
