The apparatus consists essentially of a gas exchanger and a small dialyzer. Satisfactory oxygenation of the blood has been achieved and foetuses have been kept alive and active at 38°C for 7 h after they have been removed from the uterus. The circulation both inside and outside the body is maintained by the foetal heart, and drop counters are used to record the blood flow in the umbilical arteries and vein. The venous and arterial pressures in the umbilical cord can be varied independently, and records are shown of the effects of doing so upon the blood flow through the vessels. An electrocardiogram enables continuous records to be kept of the foetal heart, and temporary failures of the circulation have been shown to cause reversible disorders of rhythm and conduction.