A Comparative Study of the Concentrations of Nonprotein, Urea, and Amino Acid Nitrogen in the Maternal and Fetal Plasmas of Sheep and Goats **

During the course of a study of placental function,' the concentration of nonprotein nitrogen in the fetal and maternal plasmas in sheep and goats was determined routinely. Although the samples were obtained during experiments which were primarily designed for other purposes, there was no reason to believe that the levels of N.P.N. would be altered. As the data indicated a difference in concentration on the two sides of the placental barrier, the study was extended to include a comparison of the urea and amino-acid nitrogen levels in the maternal and fetal plasmas as a step toward an understanding of the role of the five-layered, syndesmochorial placenta of the ruminants in the nitrogen metabolism of the fetus. The results of these comparisons, made on samples obtained from sheep and goats at known stages in the latter two-thirds of the gestation period (circa 145-150 days), form the substance of this report.