STUDIES in fetal physiology have been carried on for many years; but in the early days, the 1930's and 1940's, such work was conducted largely by a few pioneers in the field, such as Barcroft, Barron, Dawes, and Reynolds. Even though interest in this field is increasing, and pediatricians are recognizing more and more the importance of knowledge of fetal pathophysiology in the understanding and management of problems in the newborn, the study of fetal physiology has clearly developed more slowly than the study of adult physiology. This is probably due in major part to the difficulties of approaching the fetus within the uterus for experimental manipulation. In this field then, more than most, operative methodology is of paramount importance.
Up until about ten years ago most experiments in fetal pathophysiology were conducted on the exteriorized fetus, most often in sheep. As far as I am aware, the first experimental