Anaphylaxis in the Mouse Produced with Soluble Complexes of Antigen and Antibody.∗

Summary 1) Soluble BSA anti-BSA complexes formed in regions of extreme antigen excess are less anaphylactigenic for the mouse than similar complexes formed in regions of low antigen excess. 2) The hypothesis is advanced that anaphylactigenic activity of these complexes for the mouse is dependent upon their capacity to react with complement.