ABSTRACT
The presence of an extensive system of apical tubules and invaginations and enormous supranuclear vacuoles in the ray intestine is similar to the jejunum and ileum in neonatal calves (Staley eta/. 1972), the small intestine in the suckling rat (Shervey 1966, Cornell and Padykula 1969) and the duodenum in the newborn mouse (Hugon 1971 ). In certain newborn mammals, including the rat, lamb, goat, dog, cat and pig, the small intestine is transiently capable of absorbing intact proteins (Brambell 1958). This is the major method of transmitting passive immunity from the mother to offspring. In newborn animals, maternal antibodies present in milk are absorbed by the distal small intestine. Lesser amounts of maternal antibodies are received transplacentally (Brambell 1958). In the postnatal rat, this capability is gradually lost as the rate of antibody absorption falls from days 1 to 18 and is completely lost at 21 days (Halliday 1955). ln man, nearly all passive immunity is imparted transplacentally but antibody absorption can occur in breastfed infants (Leissring et a/. 1962).
