The route of antibodies passing from the maternal to the foetal circulation in rabbits

It has long been known that maternal circulating antibodies pass into the foetal blood in rabbits during the latter half of pregnancy. The allanto-chorionic placenta has been assumed to be the site of this transference, the number of tissues separating the two blood streams being reduced to a minimum in rabbits at these stages. It was shown in a recent paper that, at a stage before the establishment of the embryonic circulation, maternal circulating antibodies pass the bilaminar omphalopleur into the yolk-sac cavity. It is shown in this paper that in 24-day embryos antibodies pass from the maternal circulation by way of the uterine lumen and the yolk-sac splanchnopleur into the foetal vitelline circulation, and do not pass by way of the allanto-chorionic placenta. The method employed involved injection of immune rabbit serum either into the uterine lumen or the maternal blood and interruption of the foetal vitelline circulation of some of the embryos by ligaturing the yolk-sac stalk.