Rabbit anti-rat-brain serum immunoglobulins injected into pregnant rats on the ninth, tenth, eleventh or twelfth day of gestation resulted in a fetal resorption rate 15 to 30 times higher than that found in normal untreated pregnant rats. Human serum immunoglobulins obtained from normal postpartum mothers produced a similar percentage of fetal resorption when injected by the same routes into pregnant rats of the same gestational age. In neither of the above experiments were malformations detected among the delivered 20-day fetuses. Injection of human serum immunoglobulins obtained from mothers of children with spina bifida manifesta into pregnant rats along similar routes and periods gave comparable fetal resorption rates. Injection of the above immuno-globulin into the lumen of the uterus adjacent to implantation sites gave a low fetal resorption rate and produced varying degrees of skeletal and soft tissue malformations among the viable survivors.

The only difference which could be discerned between normal postpartum immunoglobulins and those obtained from mothers of spina bifida manifesta children was characterized in the latter by a two-fold increase in the IgG levels and the immunoelectrophoretic reactivity of its immunoglobulins with human spinal cord antigens. The developmental defects observed were: 1. Cranial-thinning and bleb formation of skull bones; widening of the foramen magnum; descent of the obex closer to the foramen magnum. 2. Skeletal-delayed or inhibited calcification of the bodies and spinous processes of the thoracic and lumbar vertebrae; widening of the vertebral canal and central canal of the spinal cord.