The recognition that permeability increases progressively along the capillaries of voluntary muscle (1) has led us to study the state of affairs in other organs. An exceedingly pronounced gradient is demonstrable in the skin of the frog, and the small cutaneous venules are even more permeable than the adjoining portion of the capillaries (2). Because of the importance of mammalian skin in water storage and regulation, we have proceeded to study this organ. The skin of the albino mouse was chosen for the purpose because the spread of dyes from the blood can be followed with special ease in it.
The Escape of Dyes from the Blood into the Skin of the BodyIn preliminary tests vital dyes of known diffusibility were injected into a tail vein of unanesthetized animals which were decapitated shortly after. The skin was found to color evenly with rapidly diffusible pigments, whereas with poorly diffusible ones, such as are especially suited to disclose local differences in vascular permeability, there was to be seen a deep staining of the tissue through which the small venules coursed, before any general coloration of the corium had taken place. The phenomenon was visible only when a skin flap was studied from its under side and even then ordinarily the subcutaneous fat prevented a clear view. To do away with it mice were kept on a reduced ration until they had become thin. They yielded pictures that were highly informative.