THE PLACENTA OR AFTERBIRTH.
Whenever conception occurs, a soft, spongy substance is formed between the uterus and the growing ovum, called the placenta. It is composed of membrane, cellular tissue, blood-vessels, and connecting filaments. The principal use of this organ seems to be to decarbonate the blood of the foetus, and to supply it with oxygen. It performs the same function for the foetus that the lungs do for the organism after birth. It allows the blood of the foetus to come into very close contact with that of the mother, from which it receives a supply of oxygen, and to which it gives up carbonic acid. This interchange of gases takes place in the placenta, or between it and the uterus, through the intervening membranes. This decarbonating function requires the agency of the maternal lungs, for the purpose of oxygenating the mother's blood.
The placenta is attached to the uterus by simple adhesion. True, in some instances, morbid adhesion takes place, or a growing together in consequence of inflammation, but the natural junction is one merely of contact, the membranes of the placenta spreading out upon the cavity of the uterus, so that, finally, the former may be entirely removed without a particle of disturbance or injury to the latter. Formerly, it was supposed that the placental vessels penetrated into the substance of the uterus. We know now there is no such continuation of the vessels of the one into the other. The decarbonation of the blood requires the placental and uterine membranes to be in contact with each other.
If the union were vascular, the mother's blood would circulate in the foetal body, and the impulses of the maternal heart might prove too strong for the delicate organism of the embryo. Besides, the separation of the placenta from the uterus might prove fatal to both parent and offspring. The placenta is only a temporary organ, and when its functions are no longer required, it is easily and safely removed.