The generic term "allergic" is reserved for the entire group of processes in which a coagulant antibody takes part. The reaction now against the antigen antibody complex is a typical antiheterogeneous response. A fundamental difference exists, however, between the antiheterogeneous reaction in the primary toxic stage and the reaction which occurs when the heterogeneous factor is a complex antigen coagulant antibody usually with more noxious character than the antigen alone. It is the nature of the antigen antibody, the result of the bond of the coagulant and the antigen, which gives it the allergic character. This fact explains why, although we can possess specific immune serum able to neutralize an antigen alone, this will not influence the allergic response. Already bound to a coagulant antibody, the antigen cannot be bound again and consequently neutralized by another antibody. The specific neutralizing serum will have no effect upon the antigen coagulant antibody complex already formed and consequently will have no effect upon the processes induced by this complex. The immune serum does not influence the allergic manifestations which represent the response to antigen coagulant antibody complexes. This would theoretically explain the favorable effects of a specific serum upon a condition which is in the toxic primary stage, where the antigen intervenes as such, and the lack of such favorable effects in the allergic stage, where the antigen is representing only a part of a complex new noxious formation.

This mechanism would also explain why the same immune serum, although without curative effect upon the allergic stage of a condition, will have preventive activity. Before the onset of the allergic stage—that is, before the coagulant antibodies have appeared—the active immune serum will bind and neutralize the antigens still free in the organism. Under these conditions, when coagulant antibodies appear, the antigens are no longer available to be bound by them to form the noxious antigen coagulant antibody complexes. Without curative action, immune serum is effective as a preventive only when administered prior to appearance of coagulant antibodies.

An important factor for the allergic response is the time of liberation of coagulant antibodies. Generally, a period of 6 to 8 days is required. Under special circumstances, as in cases in which the organism has manufactured the same antibodies in the past, the time necessary for their appearance is reduced even to 4 days. In other cases, for certain antigens or for older subjects, the time may be as long as 14 days or even longer. For certain antigens, or under special circumstances, the body appears unable to make coagulant antibodies at all. In that case, no allergic manifestations appear.

It must be emphasized that antibodies will be liberated even if the antigen is no longer present. The presence of antibodies alone does not give rise to any reaction and their appearance will pass without any manifestations. However, they can persist under certain circumstances for months or years and become a potential source of abnormality. At any time if the same antigen becomes present in the body, the coagulant antibody will form the allergic bond with it. The body will then react against the newly formed complex with an antiheterogeneous response. If this occurs in the blood or central nervous system, it can appear as an immediate violent reaction which corresponds to anaphylactic shock. It is the intensive first phase of the diphasic phenomenon which kills in anaphylactic shock. Such shock can be easily produced in animals as passive anaphylaxy by making coagulant antibodies and antigens available concomitantly in the blood.