Anaphylactic shock occurs (in rabbits) when the usual procedure for the production of passive anaphylaxis is reversed; that is, when an animal previously treated with antigen receives the corresponding antiserum by way of the circulating blood.
This susceptibility to the action of anti-horse serum produced by injection of antigen reaches maximum intensity after an interval of 4 hours presumably required to permit penetration of the antigen in sufficient concentration into the tissues.
Desensitization to the action of a shock-producing dose of anti-horse serum can be brought about by repeated small doses of the same antiserum.
Anaphylactic shock and local anaphylaxis manifested by the acute inflammation of an immunized animal when injected with the antigen used for immunization (Arthus phenomenon) occur under analogous conditions; that is, when antigen and antibody meet within the tissues. The peculiar characters of these reactions are dependent upon the site of entry of the irritating agent, which is the vascular system in one instance and tissue spaces in the other, and upon the concentration of antigen and antibody within susceptible tissues.
Meeting of antigen and antibody within susceptible tissues is sufficient to explain the phenomena of local and general anaphylaxis so that it is unnecessary to assume the sudden formation of a toxic substance (anaphylatoxin).