A method has been devised to measure the spread of vital dyes in the skin of mice. Spread is greatly influenced by physiological and pathological changes which add fluid to the tissue or abstract it.

Spread is greater in the quiet, living ear than in the ear of an animal just killed. It is equally considerable in the frankly edematous ears of living and dead animals, and not greater in either case than in normal, quiet tissues. During the early stages of edema formation on the other hand, dye spread is notably rapid. It is still greater in the ears of normal animals actively moving about, and is greatest in tissues subjected to very gently intermittent changes in external pressure.

The significance of these findings is discussed.

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