The phenomenon of wheal formation (urticaria) of the skin is dependent on certain vascular phenomena, namely, dilation of the vessels and increased permeability of vessel walls, resulting in localized edema of the skin. As it has been observed that wheal formation is modified in a measureable degree in cardiac edema,1 it seemed advisable to study it in other conditions. It was hoped in this manner to obtain information as to the condition of the skin vessels, especially in relation to their permeability, in such abnormal conditions. Other methods have been used to determine vascular permeability:2 1. The distribution into the tissue of dyes injected into the blood stream. 2. Changes in the blood concentration under varying conditions. 3. The injection of fluids into the tissues and later withdrawing them and determining the changes that had taken place. 4. The determination of the blistering time of the skin.
Because