Part 2 (1/2)
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 s.p.a.ce 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 part.i.tion. 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 circ.u.mference. 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 pa.s.sing 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 ma.s.s, 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 nouris.h.i.+ng 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 a.s.sumes the entire task, and the yolk sack pa.s.ses away. Then, later, the placenta replaces the allantois, and the latter pa.s.ses 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, nouris.h.i.+ng 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 nouris.h.i.+ng.
The story of the circulation of the blood of the fetus is most interesting. Although the fetal blood is derived from that of the mother, as we have said, yet the maternal blood does not pa.s.s directly from the circulatory system of the mother into that of the fetus; nor does the blood of the fetus return directly into the circulatory system of the mother. In fact, the fetal blood never comes in direct contact with that of the mother, or vice versa. The fetus has an independent circulatory system of its own, and yet, at the same time, from the moment of the placental connection until the moment of childbirth, all its nourishment is derived from its mother.
The secret of the above paradoxical statement is made apparent when we understand the meaning of the scientific term ”osmosis.” Osmosis is ”the pa.s.sage of a fluid through a membrane”; it is a chemical process, caused by the chemical affinity between two liquids or gases separated one from the other by a porous diaphragm or substance. In the process of osmosis in the case before us, the fetal blood takes up nouris.h.i.+ng substances and oxygen from the blood of the mother, and pa.s.ses on to the latter the waste products of the fetal system, by means of pa.s.sing these substances through the thin porous membranes which separate the two independent systems of blood vessels, i. e., the system of the fetus, and that of the mother. Before birth, in fact, the fetus has its blood nourished and oxygenated by means of the food partaken of by its mother, and the oxygen taken in by the mother in her breathing. After its birth, the infant eats and breathes for itself, and thus nourishes its blood supply directly, instead of receiving it indirectly from the mother.
The Placenta begins to be formed about the third month of gestation, and continues to develop steadily from that time. At the time of the delivery of the child the Placenta covers nearly or quite one-third of the inner s.p.a.ce of the distended Uterus of the mother. The total ”afterbirth” consists of the Placenta, the umbillical cord, and the remaining membranes of the ovum, all of which are expelled after the birth of the child.
THE AMNION. An important appendage contained in the Uterus in connection with the developing fetus is that known as ”The Amnion.” This is an inner sack which forms within the womb, and which serves to enclose the fetus, and also to sheath the umbillical cord. The Amnion encloses the embryo very snugly during the early stages of its development, but it gradually becomes distended with a pale watery fluid, known as ”the amniotic fluid,” the purpose of which is to ”float” the fetus and to give it mechanical support on all sides. This fluid is composed of water carrying in solution small quant.i.ties of alb.u.min, urea, and salt.
s.e.x IN THE EMBRYO AND FETUS. It is impossible to determine the s.e.x of the embryo during its early stages. During the fourth week the first traces of the s.e.xual glands appear, but not until the fifth week can the s.e.x be determined even by the microscope. If the embryo is to become a male, certain ducts are transformed into convoluted tubules, and each is attached to the testes which have been formed from the genital nucleus.
If the embryo is to become a female, the ducts join to form the uterus and v.a.g.i.n.a, other portions being transformed into the fallopian tubes and connecting with the ovaries which have been formed otherwise. The outer genitals appear in the early stages of the embryo, but there is no apparent distinction between the s.e.xes, the external organs being the same in all cases, and consisting of a small tubular organ with a small lateral fold of skin on either side. Later, in the male, a groove appears on the under side of this primitive organ, thus forming the urethra, the s.c.r.o.t.u.m being formed from the folded skin at the side. In the female, the primitive organ ceases to develop as in the male, and thus becomes proportionately smaller, and evolves into the c.l.i.toris of the female; the two lateral folds, on each side, being transformed into the l.a.b.i.a majora, or ”outer lips” of the female external genitals.
POSITION OF THE FETUS. During the period of gestation the fetus lies ”curled up” in the bag of the amnion. The head is usually relaxed and inclined forward, the chin resting on the breast; the feet are bent up in front of the legs, the legs bent up on the thighs, the knees separated from each other, but the heels almost touching on the back of the thighs; the arms bent forward and the hands placed between them as though to receive the chin between them. The folded-up fetus forms an oval, the longest diameter of which is about eleven inches at its greatest stage of growth. Nature here shows a wonderful ability to pack the fetus into as little s.p.a.ce as possible, and in such a position as to protect it from injury, and to discommode the mother as little as possible.
The following interesting statement made by Helen Idleson, M. D., in a European medical journal several years ago, gives a very clear idea, expressed in popular terms, of the appearance and characteristics of the embryo or fetus in the various stages of its development:
”The growth of the embryo after fecundation is very rapid. On the TENTH DAY it has the appearance of a semi-transparent grayish flake. On the TWELFTH DAY it is nearly the size of a pea, filled with fluid, in the middle of which is an opaque spot, presenting the first appearance of an embryo, which may be clearly seen as an oblong or curved body, and is plainly visible to the naked eye on the fourteenth day. The TWENTY-FIRST DAY the embryo resembles an ant or a lettuce seed. Many of its parts now begin to show themselves, especially the cartilaginous beginnings of the spinal column, the heart, etc. The THIRTIETH DAY the embryo is as large as a horse-fly, and resembles a worm, bent together. There are as yet no limbs, and the head is larger than the rest of the body. When stretched out it is nearly half an inch long. Toward the fifth week the heart increases greatly in proportion to the remainder of the body, and the rudimentary eyes are indicated by two black spots toward the sides, and the heart exhibits its external form, bearing a close resemblance to that in an adult. In the SEVENTH WEEK, bone begins to form in the lower jaw and clavicle. Narrow streaks on each side of the vertebral column show the beginning of the ribs. The heart is perfecting its form, the brain enlarging, and the eyes and ears growing more perfect, and the limbs sprouting from the body. The lungs are mere sacks, and the trachea is a delicate thread, but the liver is very large. In the seventh week are formed the renal capsules and kidneys.
”At TWO MONTHS, the forearm and hand can be distinguished, but not the arm; the hand is larger than the forearm, but it is not supplied with fingers. The distinction of s.e.x is yet difficult. The eyes are prominent. The nose forms an obtuse eminence. The nostrils are rounded and separated. The mouth is gaping, and the epidermis can be distinguished from the true skin. The embryo is from one-half to two inches long, the head forming more than one-third of the whole. At the end of THREE MONTHS, the eyelids are distinct but shut; the lips are drawn together; the forehead and nose are clearly traceable, and the organs of generation prominent. The heart beats with force; the larger vessels carry red blood; the fingers and toes are well defined, and the muscles begin to be developed.
”At the FOURTH MONTH, the embryo takes the name of 'fetus.' The body is six to eight inches in length. The skin has a rosy color, and the muscles produce a sensible motion. A fetus born at this time might live several hours. At FIVE MONTHS the length of the body is from eight to ten inches. At SIX MONTHS, the length is twelve and one-half inches. The hair appears on the head, the eyes closed, the eyelids somewhat thicker, and their margins, as well as their eyebrows, are studded with very delicate hairs. At SEVEN MONTHS, every part has been increased in volume and perfection; the bony system is nearly complete; length, twelve to fourteen inches. If born at this period, the fetus is able to breathe, cry and nurse, and may live if properly cared for.
”At EIGHT MONTHS, the fetus seems to grow rather in length than in thickness; it is only sixteen to eighteen inches long, and yet weighs from four to five pounds. The skin is very red, and covered with down and a considerable quant.i.ty of sebaceous matter. The lower jaw, which at first was very short, is now as long as the upper one. Finally, at term, NINE MONTHS, the fetus is about nineteen to twenty-three inches long, and weighs from six to eight pounds. The red blood circulates in the capillaries, and the skin performs the functions of perspiration; the nails are fully developed.”
Another writer says: ”There is a superst.i.tion that a child born at eight months is not as liable to live as if born at seven months; indeed, many suppose that an eight months' child never survives. Facts do not prove this idea to be correct. Personally, I have known several eight months'
babies to live and do well, and I believe that their chance of life is much greater than if born at seven months.”
Children born in the seventh month of gestation are capable of living, though great care is required to rear them for the first few months after birth. The ”incubators” now so common in large cities have greatly increased the chances of the ”seven months' child,” and, for that matter, of those born even earlier. There are a number of cases of record where children have been born after six months of gestation, and a few even before the six months, but these cases are rare and unusual, and such children usually die soon after birth.
The following table, given by a good authority, shows the average length and weight of the human embryo and fetus: