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JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org. All use subject to http://about.jstor.org/terms CHILD DEVELOPMENT pears not merely to refute this position but indicates a remarkable stability in the infant's circulation, and that the heart assumes its adultlike function within a short time after birth. On the subject of closure of the fetal channels, Ribble evidently refers to the obliteration of the ductus arteriosus, the foramen ovale, and the ductus venosus, since others of major importance are closed by tying of the umbilical cord.The ductus arteriosus: Evidence that the ductus arteriosus closes functionally within the first few minutes after birth, probably within the first five, is indicated by the following:[. Kennedy and Clark (44), working with guinea pigs, have shown that the increased oxygenation of the blood at birth causes the ductus arteriosus to close by sphincterlike contractions. The histological work ofHayek (80) confirms these findings. The former authors have demonstrated that the contraction is not a neuromuscular reflex, since it still takes place in the absence of all innervations (45).2. Barclay, Barcroft and others (4, 5) have shown by X-ray cinematography that the ductus in the lamb closes within about five minutes after delivery. They also have shown (6) that only a few minutes are required for the newborn organism to transform the oxygen saturation of its arterial blood from 50 per cent or less to 75 or 8o per cent, a concentration which is not too infrequently found in people living at high altitudes. Ninety per cent oxygen saturation is reached within a few hours. (72) found on measurement of oxygen concentration of the arterial blood of 31 newborn infants, that for some it was in the adult range within one half hour, for all but two it had risen above 90 per cent saturation in two hours, and for these it was above 90o per cent by three hours. In order for the oxygen concentration of the blood to be this high, the ductus must be functionally closed, otherwise, blood by-passing the lungs would have considerably lowered the oxygen saturation (31). According to Arey (i) the ductus is structurally impervious by a postpartum age of one month. Smith and KaplanThe foramen ovale: The foramen ovale is functionally closed by the septum primum being held in apposition with it by a relatively greater left ventricular blood pressure. The foramen ovale closes functionally within the first few hours after birth as the following studies indicate: r. The findings noted above (72) that the oxygen saturation of the blood exceeds 90o per cent in the first three postnatal hours in normal infants indicates that closure must have occurred, since otherwise blood by-passing the lungs would have resulted in a lower oxygen s...