The Prospective Mother, a Handbook for Women During Pregnancy

by J. Morris Slemons

THE DEVELOPMENT OF THE OVUM

The Germinal Cells—Fertilization—The First Steps in Development—
The Reaction of the Uterus—The Amniotic Fluid—The Placenta—The
Umbilical Cord.

Pregnancy, besides changing the external form of the body, causes sensations—as for example those due to fetal movements—which are so distinctive that they cannot escape notice. These obvious evidences of approaching motherhood naturally lead thoughtful women to wonder about the hidden mechanism of development, a mechanism which, of itself, causes no sensation whatever. It is for this reason, perhaps, that a prospective mother's imagination is so apt to be unusually active, often picturing absurd conditions as responsible for one symptom or another. Those who give free play to the imagination in regard to the formation and progress of the embryo are pretty certain to arrive at erroneous if not grotesque conclusions; for example, they may attribute a protracted pregnancy to the child's having grown fast to the mother, a situation that cannot arise.

Of course it is not essential that a prospective mother should understand what is happening within the womb. And upon those who prefer to be ignorant of the mechanism of development I would not urge another point of view, for not ignorance but the unchallenged acceptance of "half-truths" and of totally incorrect explanations is the chief source of harm. On the other hand, my own experience has taught me that women who wish to know about development should be told the truth. In accord with this is the fact that I never have more satisfactory patients than those who have previously been trained nurses and who, in preparing for that profession, received instruction concerning the reproductive function of human beings.

A description of development, in order to be perfectly clear, must begin with a word about the fundamental structure of the adult body. Everyone knows that the various parts of the body perform different functions; but not everyone, perhaps, realizes that, in spite of their different functions, all the organs of the body are composed of similar structural units, known as cells. Of course, cells are definitely arranged according to the use for which the tissue that they chance to compose may be designed; they have, moreover, distinctive individual peculiarities which can be easily recognized under the microscope; but the essential features of the cells remain the same, wherever they may be located. That is to say, each cell is a minute portion of living matter, or protoplasm, separated from its neighbors by a partition, the cell-membrane; each has its own seat of government, the nucleus, located near its center; and each, to all intents and purposes, leads an individual existence.

THE GERMINAL CELLS.—Many of the cells in the human body are able to produce others of their kind. This they do virtually by growing and splitting in half; cell-division, as this splitting is called, really represents reproduction reduced to the simplest terms. Most cells can do no more than produce units like themselves. The bodies of women contain, however, a type of cell which possesses a far more wonderful power. Provided the requisite conditions for such development are met, these cells are capable of developing into human beings. Each of these remarkable units is called an Ovum, or egg-cell, and represents one variety of the germinal cells. But the other variety, represented by the Spermatozoon and developed only in the male sex, is also required for the production of a human being.

Every ovum originates in the ovaries. These are organs peculiar to women, having the size and shape of large almonds, and placed in the lower part of the abdominal cavity. Though the ovaries are two in number, one alone is sufficient for every requirement of health. It has been estimated that the ovaries together contain at the time of birth about 40,000 ova, distributed equally between them. Since less than 500 ova are required to insure regularity in the menstrual function, it is clear that, if the surgeon finds it necessary to remove one of the ovaries, the other will provide abundantly for menstruation and for the bearing of children. Although every ovum that will be produced as long as a woman lives has already sprung into existence by the time she is born, not a single one ripens for from twelve to fifteen years. The ripening process begins about the time of puberty, and, unless suspended through the occurrence of pregnancy, continues until the menopause. During this period, which is also characterized by the periodical appearance of menstruation, one ovum ripens each month; sometimes, though rarely, several ripen at once, and this tendency is partly responsible for twins.

The human ovum is a tiny structure, measuring about 1/125 of an inch in diameter. With the naked eye it can barely be seen; magnified by the microscope it appears as a little round bag made of a transparent membrane. Briefly described, the ovum is a single cell. That is, it belongs to the simplest class of anatomical structures, and is one of the millions upon millions of units that make up the body. It contains a nucleus surrounded by nutritive material, the yolk. Yet the quantity of yolk is exceedingly small. In this particular the human ovum differs notably from the egg of birds, as it does also in that it lacks a shell. Obviously, a shell would not only be useless to an embryo developing within the body of its parent, but would shut off the nourishment, which, since the ovum contains so little, must necessarily be provided by the mother.

When the ovum has ripened, it becomes detached from the ovary, and enters a fleshy tube about the size of a lead pencil, known as the oviduct. There are two of these tubes, one running from the neighborhood of each ovary; both enter the uterus, but on opposite sides. The ovum travels down the tube which corresponds to the ovary where it originated. The journey is fraught with momentous consequences, for it is during this passage through the oviduct that the fate of the ovum is determined. If it is to develop into a living creature, a great many conditions must sooner or later be fulfilled; but there is one which must be promptly satisfied. Shortly after leaving the ovary the ovum must receive the stimulus to live and grow; otherwise it will quickly wither and die. This vital stimulus can be imparted only by the spermatozoon.

The male germinal cell is like the female cell in the possession of a nucleus; in other respects it is very different. Longer but much narrower than the ovum, the tiny arrow-shaped spermatozoon is particularly distinguished by its active motility, for it has a tail that propels it. The human male cell must travel some distance to reach the point where it can meet a ripe and vigorous ovum; and since the journey is not without danger to its life, Nature has provided that exceedingly large numbers of the male cells shall be deposited in the vagina at the time of the marital relation. In this way, it is made sure that some of them will travel up through the uterus and oviducts, arriving in the neighborhood of the ovaries.

FERTILIZATION.—Convincing observations upon the lower forms of life, especially upon fishes, have shown that when the germinal cells come near to each other, the ovum attracts the spermatozoon. The power of attraction which the ovum exerts may be likened, most simply, to the influence of a magnet upon iron-filings. While there has been no opportunity to observe such attraction between the parent cells of human beings, its existence is not open to doubt. And it is practically certain that these cells meet in the oviduct, even in that portion of it which receives the ovum just as it leaves the ovary. Thither a number of the male cells have traveled by their own activity; several come in contact with the ovum and one, but only one, actually enters it. Almost at the moment when they touch, the two cells unite so intimately that all trace of the spermatozoon is lost. Fertilization of the ovum, as this event is scientifically termed, has as its main purpose the uniting of the nucleus of a male germinal cell with the nucleus of the female germinal cell. This detail has been carefully studied; we know that the nuclei quickly blend into one, and that the particles of living matter contributed by the male animate the female cell with a new and wonderful activity.

In our every-day way of speaking, fertilization means conception; it is the instant in which a living being begins its existence. There is no longer the slightest excuse for confusion regarding the period at which the life of the unborn child begins. Before the significance of fertilization was understood, it was perhaps not unreasonable to believe that life began with quickening or about the time the fetal heart-sounds could be heard. But now we must acknowledge that both these ideas were incorrect. The animation of the ovum at the moment of conception marks the beginning of growth and development which constitutes its right to be considered as a human being.

Individuality, hereditary traits, sex—all these, we may be sure—are unalterably determined from the moment of conception. The germinal cell forms the total contribution of the male parent to pregnancy; therefore no other opportunity for him to influence his progeny presents itself, and the substance which enters the ovum at the time of fertilization must be the basis of inheritance from the father. It is equally true, as we shall see in the next chapter, that the nucleus of the ovum and the nucleus alone transmits maternal qualities. The material which conveys inheritable characters can be seen and has been identified in both germinal cells; from each of them the fertilized ovum derives equal amounts. As the parental nuclei unite, the material which they contain intermingles and establishes a new being; to attain full development, it requires nothing further from the father, and nothing save nourishment from the mother.

THE FIRST STEPS IN DEVELOPMENT.—Although the identity of the spermatozoon is lost at the moment of fertilization, its influence just then begins to be asserted. In the fertilized ovum the dawn of development is shown at first by unusual activity within and later by alterations upon the surface. Before very long the circumference of the cell becomes indented as if a knife had been drawn around it, and shortly two cells appear in place of one. These two cells in turn divide, yielding four cells which grow and divide into eight. In this manner division follows division until a multitude of cells have sprung into existence, all of which cling together in the shape of a ball. Development always proceeds in the same orderly way; evidently it is governed by fixed laws which decree that the mass shall remain for a while in the form of a ball, though the ball, at first solid, soon becomes hollow.

While these changes are taking place the growing ovum is carried down the oviduct a distance of four to six inches and finally comes to rest in the uterus, where it is to dwell during the months necessary to its complete development. The time consumed by this journey cannot be measured accurately; it may be as short as a few hours or as long as several days, but in all probability it is never longer than a week. Although the element of time is uncertain the method of transmission is well understood. Of its own accord the ovum can move after fertilization no better than before; it is never capable of moving itself. The active agent of transportation is the oviduct, which has been fitted for this purpose with millions of short, hair- like structures that project into its interior. These are closely set upon the inner surface of the oviduct; their outer ends are free and continually sway to and fro like a wheat field on a windy day; and by their motion they create a current in the direction in which the ovum should move, namely, toward the uterus. While passing through the oviduct, the ovum has no attachment whatever to the mother, yet development is going on all the time. It is thus made perfectly clear that development is not directed by the parent. This independence of the parent, though it continues to be one of the characteristic features of the development of the ovum, shortly becomes less evident, for communication is set up between the mother and the ovum as soon as it reaches the uterus. Unless we were warned, we might easily misinterpret the significance of this attachment to the parent. It does not permit the mother, for instance, to influence the mind or character which the child will have. The purpose of the attachment is twofold, namely, to anchor the ovum, and to arrange channels by which, on the one hand, nutriment may reach the embryo, and, on the other, its waste products may return to the mother. The mother may influence the nutrition of the fetus; but she cannot determine the kind of brain or liver her child will have; neither for that matter can she alter the development of any portion of the embryo.

After its entrance into the cavity of the uterus prepared to receive and protect it, the mass of cells sinks into the soft, velvety lining of the organ. Here it is entirely surrounded by tissue which belongs to the mother. But just before implantation takes place the architecture of the ovum is modified in such a way as to indicate the trend of its subsequent development. We left it, a hollow ball passing down the oviduct; had we examined the sphere more closely we should have found its wall composed of a single layer of cells. At one spot, however, the wall soon thickens. The thickening is due to a specialized group of cells which gradually grows toward the hollow center of the ball. A little later, if we study the structure as a whole, we find it a small, distended sac, from the inner surface of which hangs a tiny clump of tissue. The clump of cells within and the inclosing sac as well are both requisite to the ultimate object of pregnancy; yet they fulfill very different purposes. The clump within will mold itself into the embryo; the inclosing sac will make possible the continued existence and growth of the embryo by securing and conveying to it nourishment according to its needs. These two structures, which from now on constitute the ovum, can best be considered separately and in the order of their development. We shall therefore first study the sac and in the next chapter the embryo.

For a time after this sac, or ball, as you may choose to think of it, becomes implanted in the uterus, every part of its wall shares in the responsibility of procuring nourishment for the embryo. On this account the wall, or capsule, is for several weeks the most conspicuous part of the ovum. Its position is naturally advantageous, for, since it forms the outermost region of the structure and comes into immediate contact with the tissues of the mother, it has the first opportunity to seize and appropriate nutriment. Consequently, while there is still relatively little development in the embryo, the capsule of the ovum gives evidence of rapid extension; the wall becomes thicker, and the circumference of the sac increases. The significant thing about this growth, however, is the fact that it does not progress evenly. At some points cell-division is more active than at others, with the result that the surface of the ovum speedily loses its smooth, regular outline. Projections from the capsule 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 wall of the sac, it will be recalled, was originally of the same formation throughout; but when the ovum became imbedded in the womb, that part of its capsule which remained in permanent contact with the mother's blood underwent special development, whereas the rest of the capsule gradually pushed away from its primary position and, becoming stunted in its growth, even lost to some degree the development it had attained. This latter portion, the veil that passes from the edge of the placenta, is formed of the two membranes we have mentioned, namely, the chorion and the amnion.

The placenta is, for the most part, a highly developed portion of the chorionic membrane, which became specialized simply because it happened to receive the best supply of blood. At the time of birth the placenta measures nearly an inch in thickness, is as large around as a breakfast-plate, and generally weighs a pound and a quarter, that is, approximately one-sixth of the weight of the child. This relation between the weight of the placenta and of the child is regularly maintained; therefore, the larger the child the larger the placenta associated with it.

The placenta has two surfaces, easily distinguished from each other. The raw maternal surface was formerly attached to the inside of the uterus; the fetal surface, covered by the amniotic membrane, was in contact with the amniotic fluid. Across the fetal surface run a number of blood-vessels containing the child's blood, converging toward a central point at which the umbilical cord is inserted. The point at which the cord is attached affords the simplest means of distinguishing the two surfaces of the placenta.

Our knowledge as to how the exchange of food and excretory products between mother and child is carried on by the placenta has been gained chiefly through the microscope. The oldest medical writings, as we might suppose, express very fanciful ideas regarding the nature of embryonic development and the means by which it is made possible; no rational view of these matters could exist until the circulation of the blood was described by William Harvey in 1628. After this epoch-making revelation, it was accepted as true that the mother's blood entered the unborn child and returned to her own system. But that view eventually became untenable, for it was proved conclusively that there is no communicating channel between the two. For years after that, it was believed that before birth the womb manufactured milk to sustain the child, just as the breasts do afterwards; but this theory also was disproved; and, as I have said, only by the use of the microscope have we learned the truth about fetal nutrition.

When thin slices of the placenta are magnified they are found to contain countless numbers of tiny, finger-like processes; these are the villi, and they constitute the major portion of the organ. The villi seen in a mature placenta are the same as those which projected from the capsule of the young ovum, but not these alone, for many branches have sprouted from the original projections. The primary trunks with all their branches hang from the capsule of the ovum and extract nutriment from the mother's blood which surrounds them, just as the roots of a tree extract it from the soil.

The interchange of material between mother and child as carried on in the placenta can, perhaps, be made clearer if we compare one of the trunks and its branching villi to a human forearm, hand, and fingers. The hand, we will imagine, is held in a basin of water, in which, by turning on a spigot and leaving the outflow unstopped, we have arranged that the water changes constantly. In terms of this illustration, the water corresponds to the mother's blood, rich in oxygen, mineral matter, and all other kinds of essential nutriment; and the fingers are the villi. The blood-vessels in the fingers, to go a step farther, represent the blood-vessels which exist within the villi, connecting with the umbilical cord, and passing by that route to the body of the child. The blood which thus circulates through the villi, it is important to emphasize, is the child's blood; it cannot escape through the coating of the villi, just as our blood cannot escape through the skin of the fingers. Similarly, the mother's blood cannot enter the child; the two circulations are absolutely separate and distinct.

It must be noticed, moreover, that the maternal blood not only brings to the surface of the villi everything the child needs, but it also takes away the waste products of fetal life. Let us select one of the foodstuffs necessary for the unborn child, and follow its course so far as it relates to fetal nutrition. The mother's blood brings sugar, for example, from her intestinal tract to the surface of the villi; through the coating of the villi the sugar passes into the fetal blood, is carried to the fetal heart, and distributed to the various fetal organs. They burn it, deriving heat and energy, and in return give off waste products, namely, carbonic acid gas and water, which are taken up by the fetal blood, borne back to the placenta, and pass again through the coating of the villi into the mother's circulation. These waste products are then transported to the mother's lungs and to her kidneys, and are finally thrown off from her body. Before the child is born, therefore, the placenta, which is an aggregation of villi, acts as its stomach, intestines, lungs, and kidneys.

In every pregnancy the placenta serves in this way as an organ of nutrition, arranging for the passage of food from the mother's blood to the fetal circulation. Occasionally, it is interesting to observe, the placenta performs a very different function, namely, the protection of the unborn child from diseases that may attack the mother. It is able to afford such protection, because the coating of the villi is not permeable to all sorts of substances. In order to pass through their walls, material must be in solution; solid bodies, therefore, are denied admission to the fetal circulation. The most significant result of this restriction is, perhaps, that so long as the coating of the villi remains intact and healthful, bacteria cannot gain access to the unborn child. Since in health there are no bacteria in the mother's blood, this fact has no bearing upon the average pregnancy; but in those exceptional cases in which typhoid fever or some other infectious disease appears during pregnancy, it is gratifying to know that Nature has provided an unusual defense against infection of the unborn child.

That we do not know all about the interchange of substances between mother and child must be admitted; but the essential facts, and they alone are of interest here, have been established beyond contention. There is no doubt whatever that the mother's blood surrounds the placental villi but never enters the child. The fetal blood, on the other hand, is first in the child's body, then in the villi, and then returns to the child again. It never enters the blood-vessels of the mother but passes to and from the placenta as long as pregnancy lasts.

THE UMBILICAL CORD.—This rope-like structure, familiarly known as the navel-string, which connects the placenta and the fetus, is approximately twenty inches long; its length, therefore, is sufficient to permit the newly born child to lie between the mother's knees while the placenta remains attached to the womb. The cord is about the thickness of the thumb and contains three blood-vessels, all filled with fetal blood; in two of them the current is directed toward the placenta, the third carries the blood back to the fetus after it has circulated through the placental villi. In the cord the vessels lie near together and are encased in a jelly-like substance that protects them from injury.

So far as is known; the umbilical cord performs no service other than to link the blood-vessels in the placenta with those in the fetus. Simple as this may seem, it is of paramount importance in maintaining the life of the fetus, for compression of the vessels in the cord would shut off its nutriment. Against such accident, however, perfect provisions have been made; both the amniotic fluid and the jelly-like substance which surrounds the vessels are safeguards which effectually protect the circulation from pressure that might interrupt it.

Frequently, prospective mothers are told they must not "reach up" for fear the cord will become entangled. Such a precaution is quite unnecessary. No matter what the mother does, or does not, the cord will be found around the child's neck at the time of birth in one of every three cases. It is not difficult to understand how this happens. The cord is longer than the uterine cavity and must fall in coils toward the bottom of it. Now, since the fetus is free to move it enters and withdraws from these loops, many times, in the course of pregnancy. Finally, when it takes up a position head downward, as it nearly always does, the head is the part of the fetus which passes through the coil, should one happen to lie in its path. After the head is delivered the physician always feels about the neck to discover whether a loop of cord is there. If it is, he can release it easily. This condition, since it occurs so frequently and since it so rarely produces harmful consequences, should not be considered unnatural.

After the child is born, the physician cuts the cord, and in due time the after-birth is expelled through the same passage as was the child. The expulsion of the after-birth frees the mother of all the tissue derived from the growth of the ovum, for the intricate mechanism that served to nourish and protect the embryo was almost entirely developed from the ovum itself. It is a remarkable provision of Nature that very little of the mother's tissue is cast off at the end of pregnancy; and even this small portion is promptly replaced. By about the sixth week after delivery, the wound which was made by the separation of the fetal sac has completely healed. Meanwhile the mucous membrane that underwent elaborate preparations to receive the ovum, the cavity that was adjusted to its growth, and the muscle fibers that were strengthened to insure its safe entry into the world have all regained their original state. Except for the activity of the breasts, the mother is left in the same physical condition as before she became pregnant.