At present, we know that, in spite of the creation of an infant body weighing upwards of seven pounds, a placenta weighing more than a pound, together with an increase of about two pounds in the weight of the uterine muscle, all in the short span of nine months, the expectant mother has to eat very little more during this period than she ordinarily does to maintain her own bodily functions. This suggests a highly developed economy in the use of nutritive material by maternal cells. We also know that the mother excretes waste materials for the fetus and must assume that this requires an increased, or adjusted, functional activity of her excretory organs, the skin, lungs and kidneys. Moreover, the secretory activity of the previously inactive mammary glands, in spite of their remoteness from the pelvis, suggests a nervous or chemical stimulation, or both, which occurs only during pregnancy. The changes in the =uterus= itself, however, are unquestionably the most marked that take place during the period of gestation. Those that relate to the lining have been described in a previous chapter. The change and growth in the muscle wall are amazing. New muscle fibres come into existence; those already there increase greatly in size and there is a marked development of connective tissue. The actual substance of the uterus is so increased that it is converted from an organ weighing two ounces into one weighing two pounds. From a firm, hard, thick walled, somewhat flattened body in its non-pregnant state, the gravid uterus assumes a globular outline and grows so soft that the fetus may be felt through the walls. During the first few months the =uterine walls= increase in thickness, but later they grow progressively thinner, until by the end of pregnancy they are only about 5 millimetres thick. This early growth of the uterus is doubtless brought about by general systemic changes rather than by the presence of the contained embryo. Evidence of this is found in the case of tubal pregnancies when there is a definite enlargement of the uterus during the early weeks. After the third month, however, the growth of the uterus is apparently due to pressure which the growing fetus makes on the uterine walls. =The cervix= does not enlarge as a result of pregnancy, but it loses its hard cartilaginous consistency, becoming quite soft, and the secretion of the cervical glands is much more profuse. The changes in the =vagina= are chiefly due to increased vascularity. The blood vessels are actually larger, the products of the glands are greatly increased and the normal pinkish tint of the mucous lining deepens to red or even purple. The most important changes in the =tubes and ovaries= is in their position because of their being carried up from the pelvis by the enlarging uterus into the abdominal cavity. Although they increase in vascularity, ovulation is ordinarily suspended during pregnancy.