1. A method of conservation has been demonstrated in the kidneys of winter frogs.

2. The mechanism of this conservation is an increase in the absorptive function and a decrease in the excretory activity of the tubular epithelium.

3. The excessive absorptive process may be depressed by various means. Such a depression in the tubular activity is followed by large increases in the rate of excretion of water, salts and, if present in the urine, phenol red.

4. Further evidence is thus obtained which supports the theory that phenol red is excreted chiefly through the glomeruli.

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