Phagocytic Development in the Rat **†

Although there have been numerous investigations on the macrophagic or reticulo-endothelial system of adult mammals, relatively few studies have been made on the phagocytic potentialities of fetuses and young mammals. Emmel,' in an abstract on the hematogenic activity of the pig embryos' liver, commented on the phagocytic activity of the hepatic "endothelial" cells. Phagocytic capacity of the reticulo-endothelial system is present in the rabbit.' Battagliae injected carmine into 5 dog fetuses through the umbilical arteries. Although carmine collected in the pulmonary arteries, phagocytosis by alveolar phagocytes was not evident; von Kupffer cells segregated carmine granules only rarely. Culbertson' found that rats of younger age groups phagocytosed less trypan blue than did adults. Italian investigators have made contributions in the vital staining of living human fetuses and prematures. Dellepiane16 injected colloidal mercuric sulphide into human fetuses of 3, 5, and 6 months gestational age and found phagocytosis in the liver and spleen beginning in the third month. Using Dellepiane's method, Nizza-' studied human fetuses older than 6 months gestational age. He confirmed Dellepiane's findings and concluded that phagocytic activity was more marked in the liver than in the spleen. Braccoe compared the macrophagic potentialities of fetal placental blood of premature and term babies and concluded that the premature child has less phagocytic potentialities. As far as is known, no one has attempted to investigate the reticuloendothelium in its chronological development as a macrophagic system. The