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- The Prospective Mother - 6/45 -

appear; they increase in number and in length; and by the end of four weeks the ovum, as yet less than an inch in diameter, resembles a miniature chestnut-burr. To make the comparison more accurate, we must imagine such a burr covered with limp threads instead of rigid spines.

These projections, the so-called Villi, push their way into the mucous membrane of the uterus and serve a two-fold purpose. One of their functions is to fix the ovum in its new abode; and, though the attachment is not at first very secure, it becomes stronger in the course of time and is capable of withstanding whatever tendency the activity of daily life may have to loosen it. The other, and equally important, task of the villi, the majority of which dip into the mother's blood, is to transmit substances to and from the embryo.

We have traced thus far the earliest steps in the development of the ovum. One portion, we observed, was promptly set apart for the construction of the future child; this favored portion became inclosed by all the rest of the ovum, which has a more or less spherical form and is technically called the fetal sac. The first duty of the sac is to take root in the womb, and the second, no less vital, is to draw nourishment from the mother. But neither of these functions can be performed without the participation of the uterine mucous membrane, the soil, as it were, in which the ovum is planted. We must now learn how the maternal tissues assume the responsibility placed upon them.

THE REACTION OF THE UTERUS.--The womb, which is small before marriage, is converted by pregnancy into the largest organ of the body. The virginal uterus, shaped somewhat like a pear, and placed with apex downward, is carefully protected within the bony basin between the hips, which is commonly called the Pelvis. The upper and larger part of the organ, known as the body, lies at the bottom of the abdominal cavity; the lower part, the neck, projects into the vagina. The cavity inside the womb communicates above with the two oviducts and terminates below in a canal which runs through the neck and opens into the vagina by an orifice known as the mouth of the womb.

Pregnancy modifies every portion of the womb in one way or another; but the most profound alterations occur in the body, in the cavity of which the ovum has come to rest. During the forty weeks of gestation the organ grows in weight from two ounces to as many pounds; from three inches in length it increases to fifteen inches; and its capacity is multiplied 500 times.

The mucous membrane which lines the cavity of the uterus responds to the stimulus of pregnancy in a characteristic manner and with a single purpose, namely, to promote the development of the ovum. In connection with menstruation we noted that this membrane periodically prepares for the reception of an ovum. And if the expected ovum has been fertilized, its arrival is followed by arrangements for its protection and nutrition which are far more elaborate than the preparations for its reception. Within a few weeks the mucous membrane becomes half an inch thick, that is, about ten times thicker than it was; and all the elements entering into its composition, become unusually active. The blood-vessels are congested; the glands pour out a more elaborate secretion; and certain cells lay up a bountiful store of material to be drawn upon in the formation of the embryo and the building up of the structures that promote its development.

The ovum is as likely to find a resting place at one spot as another upon the surface of the uterine mucous membrane. The whole of that surface has been made ready to receive it; yet the area actually required to imbed the tiny object is extremely small. As the ovum escapes from the oviduct and enters the womb, it is smaller, in all probability, than the head of a pin. For at least a week after its coming, diligent search is necessary to find the site of implantation. Insignificant as it is at first, however, the region of implantation later becomes very prominent, for it undergoes a transformation that the rest of the mucous membrane does not share. That is to say, it becomes the point of attachment of the Placenta, an organ that has the very important function of drawing upon the resources of the mother's blood. As the ovum sinks into this especially prepared bed, the villi are formed. They break open the adjacent capillaries of the mother, thus diverting her blood from its accustomed course. The blood collects in microscopic lakes in contact with the capsule of the ovum, and from them flows back into the mother's veins. Through the veins it returns to her heart, by which it is distributed through the arteries to the various regions of the body. The tiny lakes, in which the villi hang, are thus made a part of the mother's circulation and as such are regularly replenished with purified blood. By this means the ovum receives a rich supply of nutriment, and as a natural consequence its growth is rapid.

Before very long the diameter of the ovum is greater than the depth of the mucous membrane which surrounds it. Consequently that part of the membrane which covers it is pushed into the uterine cavity, as the ground is raised by a sprouting seed. Growth continues, the bulging increases, and extensive alterations are wrought both in the womb and in the capsule of the ovum. One of these alterations will be more easily understood if we still think of the ovum as a seed, for it grows away from its roots just as plants do. Most of the capsule, therefore, is removed step by step farther from its source of nourishment, for the maternal blood-vessels do not follow the expanding sac but retain their original position at its base. Partly on account of the lack of nutriment thus occasioned and partly on account of the distention caused by the contents of the sac, atrophy occurs in the distant portions of the sac's wall. As a final result of these two factors, the maternal tissue which covers the ovum becomes thinned and stretched; it is pushed entirely across the uterine cavity; and by about the twentieth week meets the opposite side of the cavity, to which it becomes adherent. Subsequently, the sac which incloses the embryo becomes everywhere fastened to the inner surface of the uterus and completely fills the uterine cavity.

THE AMNIOTIC FLUID.--The great enlargement of the uterus which is so marked a characteristic of the latter part of pregnancy is due in a measure to the luxuriant blood-supply, for better nutrition always causes growth. In a far larger measure, however, it is due to distention for which the product of conception is responsible. Beside the fetus the inclosing sac also contains a considerable quantity of fluid. This fluid, called "The Waters" by those who have no special knowledge of anatomy, is technically designated as the Amniotic Fluid.

In the earlier months of pregnancy the amniotic fluid is not abundant; later it increases rapidly, so that by the end of the period it measures about a quart, and frequently even more. The slightly yellow amniotic fluid is itself clear, but small particles of dead skin and other material cast off from the surface of the child's body are floating in it, and may cause turbidity. The absence of odor supports the view that this fluid is not the child's urine. The evidence thus far adduced, though not absolutely conclusive, gives good reason to believe that "the waters" are secreted by the inner side of the sac which incloses the fetus. Very early in pregnancy this sac becomes a double-walled structure; and, though its layers are intimately blended, and together measure not more than 1/16 of an inch in thickness, with a little care they can be separated. The outer layer, which comes in contact with the inner surface of the uterus and has to do with the matter of nutrition, is called the Chorionic Membrane; the inner, the so-called Amniotic Membrane, is much the stronger and is devoted to the protection of the embryo, which it completely surrounds with fluid, at the same time retaining the fluid within set bounds.

The amniotic fluid performs many important duties. Perhaps the first, in point of time, is to provide sufficient room for the embryo to grow in. Later, as the fluid increases, it permits the fetus to move freely, and yet renders the movements less noticeable to the mother. Again, the amniotic fluid prevents injuries that might otherwise befall the child in case the mother wears her clothing too tight. Harmful as the practice of tight-lacing during pregnancy is, it does not, thanks to the presence of the amniotic fluid, result in the disfigurement of the child. For the same reason a blow struck upon the abdomen, as in a fall forward, is not so serious as might be thought, since the fluid, not the child, receives the force of the impact. Some physicians believe that the fetus swallows the amniotic fluid and thus secures nourishment. The fluid also serves to keep the fetus warm; or, to be more exact, protects it from sudden changes in the temperature of the mother's environment. Normally the temperature of the fetus is thus kept nearly one degree higher than the temperature of the parent.

Ultimately, the amniotic fluid assists in dilating the mouth of the womb, which remains closed until the beginning of the process that terminates with birth. The uterine contractions at the onset of labor compress the fluid; in turn the fluid attempts to escape but is held in check by the amniotic membrane, which it drives into the canal leading from the uterine cavity to the vagina. Acting like a wedge, the fluid gradually pushes the mouth of the womb wider and wider open, until it is large enough for the child to pass. The sac usually ruptures when that point is reached, the fluid escapes, and in due time the child is born. This is followed within half an hour by the extrusion of a mass of tissue--in reality the collapsed fetal sac-- which in every language, so far as I know, is named the After-Birth. An examination of this tissue at the time of delivery repays the physician, for it is important to ascertain that none of it has been left in the uterus. Our interest at present, however, is to learn how the after-birth has assisted toward the growth of the child.

THE PLACENTA.--The after-birth has puzzled scientists as well as the laity, and not until comparatively recent times have its origin, structure, and use been satisfactorily explained. Its meaning profoundly interested primitive men and stimulated their imagination scarcely less than the mystery of conception. Some uncivilized tribes believed that the after-birth was animated like the child; consequently they spoke of it as "the other half," and often saved it to give to the child in case of sickness. But generally the after- birth was buried with religious ceremony, and was occasionally unearthed later to discover whether the woman would have other children; the prophecy was made according to the manner of disintegration or some other equally absurd circumstance.

The after-birth consists of a round, fleshy cake, the placenta, to which two very essential structures are attached. One of these, running from one surface of the cake, is a rope-like appendage, the umbilical cord, which links the placenta with the fetus. The other, attached to the circular edge of the cake, is a thin veil of tissue, in some part of which a rent will be found. Now, if we lift the margin of the rent, we shall see that the veil and the cake together form a sac which we are holding by the opening. This aperture through which the fetus passed, and it was really made for that purpose, was formerly placed over the mouth of the womb; the sac itself, distended by the fetus and the amniotic fluid, was fastened everywhere to the inner surface of the womb.

It is plain that we have now in our hands the fetal sac, the development of which we have already traced from the beginning. The

The Prospective Mother - 6/45

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