If complement be injected into an animal it may act as an antigen and give rise to the formation of _anticomplement_ which may combine with it and prevent its action and is consequently analogous to antitoxin. If amboceptors as antigen are injected into an animal there will be formed by the animal’s cells _antiamboceptors_. As one would expect, there are two kinds of antiamboceptors, one for each of its combining groups, since it has been stated that it is always the combining group of any given antigen that acts as the cell stimulus. Hence we may have an “anticytophil amboceptor” or an “anticomplementophil amboceptor.” These antiamboceptors and the anticomplements are analogous to antitoxin, antiagglutinin, etc., and hence are receptors of the first order. ANTISNAKE VENOMS. A practical use of antiamboceptors is in antisnake venoms. Snake poisons appear to contain only _amboceptors_ for different cells of the body. In the most deadly the amboceptor is specific for nerve cells (cobra), in others for red corpuscles, or for endothelial cells of the bloodvessels (rattlesnake). The complement is furnished by the blood of the individual bitten, that is, in a sense the individual poisons himself, since he furnishes the destroying element. The antisera contain antiamboceptors which unite with the amboceptor introduced and prevent it joining to cells and thus binding the complement to the cells and destroying them. With this exception these antibodies are chiefly of theoretical interest. FAILURE OF CYTOLYTIC SERUMS. The discovery of the possibility of producing a strongly bactericidal serum in the manner above described aroused the hope that such sera would prove of great value in passive immunization and serum treatment of bacterial diseases. Unfortunately such expectations have not been realized and no serum of this character of much practical importance has been developed as yet (with the possible exception of Flexner’s antimeningococcus serum in human practice. What hog cholera serum is remains to be discovered).