an apparatus designed to substitute for the functions of the natural placenta and maintain the life of a fetus isolated from the mother. Gas exchange, the main function of the artificial placenta, is performed by a heart-lung machine. The blood flows into the machine and then through the umbilical vessels of the fetus, thus creating artificial placental blood circulation. Keeping a fetus alive by means of an artificial placenta makes it possible to study embryonic processes and functions in the early stages of fetal development that are not accessible to ordinary observation. Such processes include protein, carbohydrate, and hormone metabolisms and intrauterine motor activity. Artificial placentas are now used mainly to study the embryos of laboratory animals.