seems likely that chloride, as well as sodium, ma y be actively transported across
the skin of at least some amphibians, but the former process ma y not readily survive in vitro procedures.
A Chilean leptodactylid frog, Calyptocephalella gayi, like Rana esculenta, can
also accumulate sodium and chloride, independently, across its skin in v iv o (GARCIA ROMEU, SALIBIAN, and PEZZANNI-HERNANDEZ, 1969). The Na + and Cl : were
found to be exchanged, respectively, for H + and HCO J - in the body. KROGH
(1939) also found that European frogs exchanged Na + and Cl : for endogenous
solutes. Such exchanges cannot readily be demonstrated in v itro. The sk in of amphibians plays an important respiratory role as it is an avenue for the excretion of
carbon dioxide. In an aquatic environment this takes place as a diffusion of HCO J - ,
a function that would be expected to be more prominent in vivo than in vitro (GARCIA ROMEU et al., 1969). As will be described later, fish in fresh water may exchange Na " for NH 4 + across their gills (MAETZ and GARCIA ROMEU, 1964) and
it has been suggested (GARCIA ROMEU et al., 1969) the Na +/ H + substitution that
is observed in these frogs is an adaptation to a terrestrial life, and reflects the adoption of ureotelism as opposed to ammoniotelism .
The exchange of sodium between intact amphibians and their aqueous environment responds to the prevailing osmotic conditions and to the injection of certain
hormones. KROGH (1939) thus found that depleting frogs of salt by bathing them
in solutions of distilled water for several weeks enhanced their ability to accumulate
sodium and chloride. The French group at Saclay (see MAETZ, 1959) have also
shown that maintaining anurans in distilled water increases their rate of sodium
accumulation, while if the y are kept for several weeks in 0.7% sodium chloride
solutions, the rate is greatly reduced. Injections of neurohypophysial pep tides increase the rate of accumulation of sodium from solutions bathing larval and adult
Ambystoma (JORGENSEN, LEVI, and USSING , 1946; ALVAR ADO and JOHNSON,
1965), Triturus alpestris and T. cristatus (BENTLEY and HELLER, 1965), Bufo regularis (MAETZ, 1963) and Rana catesbeiana (ALVARADO and JOHNSON, 1966). The
corticosteroid hormone aldosterone has been shown to increase the net uptake of
sodium by Rana esculenta (MAETZ, 1959) and larval Ambystoma tigrinum (ALVARADO and KIRSCHNER, 1964). Such changes in the salt balance reflect actions at
several distinct morphological sites.
a) Skin
The skin of amphibians can actively take up salt from the solutions that bathe their
external surface. Sodium, and in some instances chloride, can be accumulated
against an electro-chemical gradient. Potassium is not accumulated activel y from
the external solutions. The mechanism for the active sodium transport is very efficient, for, as shown by KROGH, this ion may be accumulated from solutions as
d ilute as to - SM . Active accumulation of sodium across the sk in (In v itro and in
vivo) has been demonstrated in a number of anurans from diverse families including
the Ranidae, Bufonidae, H ylidae, Leptodactylidae and Pipidae. It has also been
shown to occur across the integument of some urodeles including Triturus alpestris
andAmbystoma mexicanus. I have been unable to find evidence from electrical
179
the skin of at least some amphibians, but the former process ma y not readily survive in vitro procedures.
A Chilean leptodactylid frog, Calyptocephalella gayi, like Rana esculenta, can
also accumulate sodium and chloride, independently, across its skin in v iv o (GARCIA ROMEU, SALIBIAN, and PEZZANNI-HERNANDEZ, 1969). The Na + and Cl : were
found to be exchanged, respectively, for H + and HCO J - in the body. KROGH
(1939) also found that European frogs exchanged Na + and Cl : for endogenous
solutes. Such exchanges cannot readily be demonstrated in v itro. The sk in of amphibians plays an important respiratory role as it is an avenue for the excretion of
carbon dioxide. In an aquatic environment this takes place as a diffusion of HCO J - ,
a function that would be expected to be more prominent in vivo than in vitro (GARCIA ROMEU et al., 1969). As will be described later, fish in fresh water may exchange Na " for NH 4 + across their gills (MAETZ and GARCIA ROMEU, 1964) and
it has been suggested (GARCIA ROMEU et al., 1969) the Na +/ H + substitution that
is observed in these frogs is an adaptation to a terrestrial life, and reflects the adoption of ureotelism as opposed to ammoniotelism .
The exchange of sodium between intact amphibians and their aqueous environment responds to the prevailing osmotic conditions and to the injection of certain
hormones. KROGH (1939) thus found that depleting frogs of salt by bathing them
in solutions of distilled water for several weeks enhanced their ability to accumulate
sodium and chloride. The French group at Saclay (see MAETZ, 1959) have also
shown that maintaining anurans in distilled water increases their rate of sodium
accumulation, while if the y are kept for several weeks in 0.7% sodium chloride
solutions, the rate is greatly reduced. Injections of neurohypophysial pep tides increase the rate of accumulation of sodium from solutions bathing larval and adult
Ambystoma (JORGENSEN, LEVI, and USSING , 1946; ALVAR ADO and JOHNSON,
1965), Triturus alpestris and T. cristatus (BENTLEY and HELLER, 1965), Bufo regularis (MAETZ, 1963) and Rana catesbeiana (ALVARADO and JOHNSON, 1966). The
corticosteroid hormone aldosterone has been shown to increase the net uptake of
sodium by Rana esculenta (MAETZ, 1959) and larval Ambystoma tigrinum (ALVARADO and KIRSCHNER, 1964). Such changes in the salt balance reflect actions at
several distinct morphological sites.
a) Skin
The skin of amphibians can actively take up salt from the solutions that bathe their
external surface. Sodium, and in some instances chloride, can be accumulated
against an electro-chemical gradient. Potassium is not accumulated activel y from
the external solutions. The mechanism for the active sodium transport is very efficient, for, as shown by KROGH, this ion may be accumulated from solutions as
d ilute as to - SM . Active accumulation of sodium across the sk in (In v itro and in
vivo) has been demonstrated in a number of anurans from diverse families including
the Ranidae, Bufonidae, H ylidae, Leptodactylidae and Pipidae. It has also been
shown to occur across the integument of some urodeles including Triturus alpestris
andAmbystoma mexicanus. I have been unable to find evidence from electrical
179