¹ From the Zoophysiological Laboratory, University of Copenhagen, Copenhagen

A method has been described in which sodium uptake may be studied in the intact, anesthetized toad. Sodium uptake is determined by "counting" the whole animal in a special chamber after suspending it in a frog Ringer bath containing radioactive Na²⁴. The effects of subcutaneous injection of the neurohypophyseal antidiuretic factor were studied with these results:

1. There was a pronounced increase in sodium influx following treatment with the hormone.

2. Sodium outflux was small in both experimental and control animals.

3. There was an increase in water uptake in both experimental and control animals after 1 hour in the bathing solution. This increase was greater in the experimental toads in which it is believed to be related, at least in part, to sodium transport.

4. Potentiometric measurements were made on the skin membrane potential of the whole animal while suspended in bathing solutions. These results were in essential agreement with those found for isolated frog skin. However, there was no apparent influence of the antidiuretic factor on the skin potential.

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