The Route by which Antibodies Enter the Circulation after Injection of Immune Serum into the Exocoel of Foetal Rabbits

Immune sera were injected into the embryonic membranes of foetal rabbits at about 24 days of age. Alternate embryos in each uterus were injected through the uterine wall, the intervening ones remaining as controls. Leakage occurs into the uterine lumen from the punctures. In the case of rabbit serum, the uptake to the foetal circulation is the same in the control, where entry is entirely via the entoderm, as in the injected foetuses, indicating that no entry occurs by way of the mesothelial surface of the splanchnopleur. Antibodies of bovine origin are excluded from the foetal circulation as effectively when the inner, as when the outer, surface of the splanchnopleur is exposed to immune serum, at this stage.