Minute amounts of Locke's or Tyrode's solution have been brought into contact with the interstitial connective tissue of the skin of the living mouse, at atmospheric pressure, in such a manner that the blood or lymphatic vessels are not entered directly. Under such circumstances these absorbable fluids enter the tissue spontaneously. Entrance is strikingly intermittent, not continuous, and so too when very slight pressures are brought to bear on the fluids (1).
Hyperemia of the tissues, with accompanying dilatation of the blood vessels, increases the entrance of fluids at atmospheric pressure but it is still intermittent. By contrast, venous obstruction leads to intermittent backflow into the apparatus, but reflex hyperemia, following release of the obstruction, is attended by an increase of flow into the tissues in spite of the great reactive dilatation of vessels. The inflow is also intermittent.
If the skin is deprived of circulation, fluid does not enter it at all at atmospheric pressure, though it moves in regularly and continuously if slight pressure is put upon it. Edema-forming fluids, described in the text, also enter in a continuous manner when forced into the skin of either living or dead animals. So too do serum and sperm oil.
The findings indicate that the passage of interstitial fluid into the blood vessels may be intermittent under normal circumstances and its escape from them as well. The observed occurrence of intermittent flow in the blood vessels of several tissues (9, 15–25) will go far to account for the intermittent entrance of fluid into the skin.