The data we possess concerning the anatomy and physiology of pulmonary fetal circulation are relatively scarce, as is also our knowledge regarding the changes which occur after birth in the pulmonary circulation.
Investigations made recently of fetuses and newborn lambs by means of cineradiography by Ardran et al.1 demonstrated that more time is required in fetuses than in newborn animals for completely filling the pulmonary arteries with an opaque medium. Likewise, the pulmonary circulating time in newborn animals was considerably shorter than that in the fetus. Everett and Simmons,2 in their experiments on guinea pigs, used erythrocytes tagged with radioactive iron. They found that soon after birth, when the pulmonary ventilation begins, the blood volume in the lungs increases considerably and within 7 to 15 hours it increases 100%. Direct observation of the blood flow through the lungs is possible by utilization of the fluorescent technique. Reynolds,9