LESSON IV
GESTATION OR PREGNANCY
Gestation is "the act of carrying young in the Uterus, from the time of conception to that of parturition." Conception occurs at the moment of the impregnation of the ovum; parturition is the act of delivery, or childbirth. Pregnancy is "the state of being with child." The terms "period of gestation," and "period of pregnancy," respectively, are employed by medical authorities to designate the time during which the mother carries the young within her own body—from the moment of the impregnation of the ovum until the moment of the final delivery of the child into the outer world.
The term of pregnancy in woman continues for over nine calendar months (or ten lunar months)—from about 275 to 280 days, though in exceptional cases it may be terminated in seven calendar months, or on the other hand may continue for ten calendar months. The usual method is to figure 280 days from the first day of the last menstruation. A simple method of calculating the probable date of delivery is as follows: Count back three months, and then add seven days, and you will have the date of probable delivery. Example: A woman's first day of last menstruation is March 28. Counting back three months gives us December 28; and adding seven days to this gives us January 4, as the date of probable delivery. There will always be a possible margin of a few days before or after the ascertained probable date—but the delivery will very closely approximate said date. Ignore the shortage of days of February in this calculation, the same being covered by the general margin allowed.
Development of the Impregnated Ovum. In the preceding lesson we terminated our consideration of the impregnated ovum at the point at which, after the process of segmentation, the "primitive trace" had appeared. This primitive trace appears as an opaque streak, or straight line, formed of an aggregation of cells of a distinctive quality. This delicate "trace" or "streak" is the first indication of the form of the coming child. It is the basis, pattern, or mould, in or around which the spinal column is to be formed, and around which the entire young body is to be developed by the wonderful and intricate processes of dividing and reduplication, and the folding and combination of cells. From one end of this "trace" develops the head; from the other end develops the lower end of the spine. At a later stage there appear tiny "buds" in the positions at which the arms and legs should be; these gradually develop, and their ends split into tiny fingers and toes, and finally are transformed into perfect little arms and legs, miniatures of those of the adult human being.
The term "the embryo" is employed to designate the developing young creature in the earlier stages of its development, particularly before the end of the third month of its existence. After the end of the third month the embryo is called "the fetus." In the short space of 280 days the young creature evolves and develops from a single simple cell into a complex organism—a perfect miniature human being. Nature works a wonderful miracle here, and yet so common is it that we take it all as a matter of course, and lose sight of the miracle. From the most simple forms are formed in the developing creature the most complex organs and parts. The heart is formed from a tiny straight line of cells, by enlargement and partition. The stomach and intestines, likewise, develop from a tiny straight line of cells arranged as a tiny tube—the stomach is formed by dilation of one part of the tube, while the large intestine experiences a similar though lesser distention and a greater growth in length; the smaller intestines being formed by growth in length and circumference. The other organs evolve from similar simple beginnings.
The embryo is nourished during its earlier stages by means of the "yolk sack," or "umbilical vesicle," which is outside the body of the embryo, being joined to it by means of the umbilical duct. This yolk sack (originally formed by a "drawing together" in the ovum, which thus separates itself into two portions or areas) is an important feature of the life of the embryo, as it nourishes and sustains it in its earlier stages. Blood vessels form in this yolk sack, and after a time its fluid is absorbed, and after the third month the sack gradually disappears.
After the passing away of the yolk sack, the embryo is nourished and sustained by the "allantois," another peculiar sack which is formed. This sack readily becomes filled with blood-vessels, and serves to nourish the embryo by sustenance obtained from the body of the mother through the walls of the Uterus, a direct communication with the blood-vessels of the mother thus being secured. The blood in the embryo, and that in the mother, come into close contact, thus allowing the embryo to be nourished by the blood of the mother. After a time, in turn, the allantois diminishes and dwindles away, its offices being taken up and performed by the "placenta" or "afterbirth."
The Placenta or Afterbirth. The Placenta, or afterbirth, is a round, flat substance or organ, contained within the Uterus, by which communication and connection is established and maintained between the fetus and the mother, by means of the umbillical cord. It is a flat, circular mass, about seven inches in diameter, and weighing about sixteen ounces. It is attached to the sides of the Uterus of the mother during the period of gestation, and is expelled from the body of the mother, as "the afterbirth," after the birth of the child.
Let us pause a moment, and reconsider the several steps in Nature's plan for nourishing the embryo and fetus. In the first place, as we have seen, there is the yolk sack or umbillical vesicle, filled with a fluid which nourishes the embryo. This gradually disappears in time, and is replaced by the "allantois" which by connection with the walls of the Uterus is enabled to nourish the fetus from and by the blood of the mother. For a short time, however, the embryo is nourished by both the yolk sack and the allantois. Then the allantois assumes the entire task, and the yolk sack passes away. Then, later, the placenta replaces the allantois, and the latter passes away as did its predecessor. The placenta works along the same general lines as the allantois, but is a far more complex way and with a much higher degree of efficiency, as we shall see presently.
The placenta is connected with the body of the fetus by what is known as "the umbillical cord." The "umbillicus" or "navel" in the human being marks the place at which the umbillical cord entered the body of the fetus, from which it was severed after the birth of the child. The purpose of the umbillical cord is to contain and support the umbillical arteries and veins through which the fetus obtains nourishment from the placental substance, and through which the return blood flows. The rich red arterial blood is carried from the placenta to the fetus, and is then distributed over the body of the fetus, nourishing and building it up; the dark venous blood, laden with the waste products of the body of the fetus, is carried back to the placenta, there to be repurified and rendered again rich and nourishing.