The Relation of Antigen to Antibody (Precipitin) in the Circulating Blood

Abstract

The experiments described in this paper have been undertaken with the purpose of determining in what degree the fate of antigen introduced into an immune animal differs from that of the same antigen introduced into a normal animal. The studies of many observers indicate that injected antigen appears in the circulating blood both of normal and immune animals and some have found no difference between the two. An antigen such as horse serum or egg white which has entered the blood of a normal or of an immunized animal is demonstrable by the addition of immune serum from another animal even though, in the case of the immunized animal, its serum exhibits a high precipitin titer when brought into contact with the antigen against which the animal is immunized. The reactions indicate that free antigen and free antibody are present in the circulating blood but they do not unite to form a precipitate.