=Placenta.=—The “after-birth” is a spongy cavernous organ and has a circumference of from 20 to 24 inches. It is made up of two elements, fetal and maternal, chiefly the former. The fetal surface, to which the umbilical cord is attached, is formed by the amnion. External to the latter is the chorionic tissue, consisting mainly of finger-like processes of villi, many of which extend to the decidua. These villi are mostly vascularized. The vascular villus is made of a capillary loop, lying embedded in a connective tissue, the blood-vessels being derived from the umbilical vessels. The villi are surrounded by maternal blood, which circulates in the intervillous spaces. The maternal part is represented by the decidua serotina. Its surface is rough and irregular, being broken up into segments or cotyledons. It is made of two layers: (_a_) The deep or spongy layer, and (_b_) the compact, or layer to which the villi are attached. The decidua serotina contains large cavities or sinuses, which are formed by a dilation of the blood-vessels in the wall of the uterus. They communicate with the intervillous spaces of the placenta, and it is through the maternal blood circulating in them that nutriment is conveyed to the fetus through the medium of the villi. An interchange takes place between the fetal and maternal bloodstreams, though, of course, there is no direct continuity between them. The placenta thus has a two-fold function in acting both as an organ of circulation and of respiration. It is through the walls of the villi that this interchange of gases and fluids takes place; nourishment and oxygen passing through them to the fetus, and carbonic-acid gas and waste materials passing through them to the mother. There is no direct communication between the fetal and the maternal blood. The placenta, normally, is attached to the contractile part of the uterus, and on its separation the blood-vessels are closed by the contractions of the uterine wall. The placenta may be divided into two or more portions, or one or more of its cotyledons may be detached from the rest of the organ and have their own vascular supply. The importance of this lies in the fact that after the placenta is expelled these isolated masses may be left and give rise to hemorrhage or blood-poisoning. SYMPTOMS OF PREGNANCY. =Suppression of the Menses.=—The cessation of the periods may be due to other causes, but it is usually the first indication of pregnancy. Conception may take place and menstruation yet continue. It usually occurs but once or twice, and then only where conception took place immediately before an expected period. =Morning Sickness.=—Nausea and vomiting continued for any length of time is almost a certain sign of pregnancy. It may begin as soon as conception takes place and last for many months; sometimes it may occur toward the end of pregnancy, or occasionally not at all.