Abstract
When proteins such as horse serum or crystalline egg albumin which have been selected because they produce the phenomena of immunity are introduced into a normal animal they diffuse widely in the tissue, enter the blood stream, and are disseminated throughout the body. The same substances introduced into an immune animal are fixed at the site of entry and are not found in the blood. When protein is injected into the skin of an immune animal acute inflammation (Arthus phenomenon) occurs at the site of injection and brings about destruction of the foreign substance.