CHAPTER VI.

GENERATION.

Generation is effected in the human species through the medium of the two sexes; to effect it there must be the actual contact of the male semen, or its spermatozoa, with a healthy Graafian vesicle.

In CONCEPTION the SPERMATIC FLUID is furnished by the male. When this is examined under the microscope it exhibits a great number of little bodies, which are moving; these are termed spermatic animalcules, or spermatozoa. These are met with in all animals capable of reproduction, and they do not appear in the human species before puberty.

The ovule furnished by the female is existent in the ovary at the marriageable period. Fecundation takes place in the ovary; probably, sometimes, also in the tube or uterus when the ovule is passing out after menstruation.

Ordinarily the fluid ejaculated by the male must reach the uterus, and in some way be conveyed to the ovaries through the Fallopian tubes to produce fecundation.

It is believed that, as the consequence of copulation, the semen is thrown on the neck of the uterus; that it is carried forward, first, by the movements proper to the uterus and tubes; second, by the movements proper to the spermatozoa till it reaches the ovum, generally in the ovary; that it enters the ovum, and that then fecundation takes place.

Upon being impregnated and the vesicle bursting, the ovum is grasped by the free extremity of the Fallopian tubes, which is in contact with the ovary, the ovum passes from the ovary to the canal, is pressed onwards by the peristaltic motions of the tube through the duct, and finally reaches the uterine cavity; there it continues to grow during the ordinary term of gestation. After two hundred and seventy days the ovule has developed into a child, and is expelled through the natural parts of generation. When gestation proceeds in this manner, it is said to be normal, or good, or uterine; sometimes (though very seldom) the ovule is arrested at some point in its passage, and is developed outside of the womb; this is termed an _extra uterine pregnancy_.

The time at which conception is most likely to occur is that immediately following the flow of the menses; it may take place immediately before the flow, and sexual intercourse may be fruitful even when it takes place in the middle of the interval between the sexual periods, though the latter is unusual.

When conception takes place a few days or a few hours before the period, it is not followed by the menstrual flow.

UTERO-GESTATION.

At each menstrual period the bulk or size of the uterus is for the time increased, and if conception takes place about that time, the excitement maintains and soon increases the enlargement. The mucous membrane becomes almost doubled in thickness, and when the ovule arrives in the womb, it finds it filled with the membrane, the whole uterus is congested, its vessels enlarge, and are filled with blood, many which were invisible before are now filled with red blood, and the whole form an intricate network on the surface, and in the substance of the organ; the coats of the arteries increase in thickness; the coats of veins are thinner, and admit of still greater distention; the nerves increase in size, and may be seen accompanying the blood-vessels, and there are changes not only in the volume, but in the shape, situation, direction, and relations of the uterus.

The organ increases slowly in size during the early. months of pregnancy, and more rapidly in the later. The walls are distended, however, not mechanically from the development of the ovum, but simultaneously with it, and from a physiological cause; in shape it becomes rounder, and towards the end of pregnancy it has an ovoid form. Simultaneously there is an alteration in its position; at first the neck subsides towards the floor of the pelvis; the presence of the rectum may incline the fundus to the right and the neck to the left; about the fourth month the uterus rises above the superior strait; at four months the fundus uteri is two or three fingers in breadth above the pubis; at five months it is within one finger’s breadth of the umbilicus; between the fifth and sixth month it passes the umbilicus; at seven months it is three fingers’ breadth above the naval; at eight months it is four or five above, but it does not rise higher during the last month. While it is rising it follows the direction of the axis of the superior strait; afterwards it inclines to the right oftener than to the left.

At term, the superior part of the uterus is in contact with the abdominal walls usually, but sometimes there may be some of the intestines interposed between them.

At full term the parietes of the womb are thicker than in the unimpregnated condition; at the point corresponding to the insertion of the placenta, thinner at the neck, and otherwise it retains about its original thickness.

The uterus increases about forty times in weight during pregnancy; at term it weighs about twenty-four ounces, and its length is from twelve to fourteen inches, its breadth from nine to ten, and its depth, antero-posteriorly, eight to nine inches.

The os uteri, after it is in the gravid state, becomes somewhat swollen, but soft and cushion-like. This softening is at first superficial. Towards the end of the third month, the lips of the os tincæ are softened throughout their whole thickness, and the softening increases from below upward.

The _neck of the uterus_ seems somewhat elongated at the first, but at the commencement of the sixth month the length of the cervix seems to diminish; there is, however, no considerable shortening until the middle of the eighth month; during the last fortnight of pregnancy it diminishes very rapidly, and finally is totally effaced.

In primapara the os tincæ is rounded at first, and is not dilated. In females that have had children the external orifice is widely open, and the cavity in the neck is funnel-shaped, continuing to increase until it reaches the internal orifice.

As gestation progresses the texture of the uterus changes. The peritoneum spreads out in all directions without a decrease in thickness; the mucous coat becomes apparent, it grows redder and more vascular, and its folds disappear; the glands of the body of the womb grow longer; the middle coat is enlarged by the increase in size of always existing muscular elements, and the formation of new fibres and increased connective tissue. There is, towards the end of pregnancy, an astonishing development of the vascular system; the lymphatic vessels acquire considerable calibre, and the nerves are developed in every way, although the neurilemma is most affected.

The changes developed in the uterine mucous membrane are of especial interest. Its vascularity is greatly increased during menstruation, the glands are enlarged, the membrane thickened, thrown into folds and becomes of a violet color; this condition continuing until the ovule is discharged, or until the last of the menstrual period. The fecundation of the ovum will maintain and increase this vascular condition of the membrane. Its vessels are so enlarged as to cause small effusions beneath the epithelium, which gives to the internal surface a spotted appearance; after two or three weeks it is still more mottled, more puffed up, and furrowed with folds and wrinkles. This membrane is the _decidua_, which is afterwards expelled, with other contents of the uterine cavity.

The DECIDUA REFLEXA is a fold of the decidua in which the fœtus is enveloped, and both of these membranes, which are at the last expelled with the fœtus, are developed from the uterine mucous membrane. The uterine decidua, after the second month, grows thinner, and its folds are gradually effaced; after the fifth month it is only one twenty-fifth of an inch in thickness, and it is still thinner at the termination of pregnancy. At the fifth month it is separable from the uterus, and the first trace of the new membrane which is to replace the decidua may be detected under it. A partly uterine membrane may be thrown off when an abortion occurs, during the early months of pregnancy.