INSEMINATION.--CONCEPTION.
This act appears to occur in the human species in the first third of the tube; at least this is the case among animals; probably it occurs much less fre quently in the uterus. The process consists in reality of the penetration of the ovum by only one spermatozoon, and the changes which are pro duced in the interior of the ovum by this penetration furnish the impulse for the formation of a new being. This process, however, is not so sim ple as has been supposed. Manifold changes of the egg precede the meet ing of the two procreative elements. It is well known that among many animals, the process of segmentation has gone on to a certain degree in the ovary without previous impregnation, an occurrence which had always been thought to be dependent upon the penetration of the spermatozoa into the ovum. We know now, that at the approach of the semen, the blastodermic vesicle changes its location, moving from the interior to the surface of the yolk; that it divides here, throws out a part of its substance from the yolk while the remainder, as the so-called ovum nucleus, returns to its former position, whereby a change in the granular division and pigmentation of the yolk is produced. The entrance of the spermatozoa into the ovum is also accompanied by noteworthy appearances. Fol noticed, in sea-stars, that only one spermatozoon penetrated an ovum, and that as soon as this had occurred, a thickening of the enveloping mem brane was instituted to prevent others from penetrating; should the lat ter occur, however, in some exceptional way, the process of development of the impregnated ovum is disturbed. It has also been proven (Neu nangen) that the yolk sends out a projection towards the penetrating spermatozoon, with which it unites, whereupon the spermatozoon is en. larged, and converted into the so-called spermatic nucleus. It is also proven that the spermatozoon and blastodermic vesicle are blended with each other, and that the constituent parts of this new formation are formed in the nucleus of the germinative vesicles. These extremely complicated processes are indeed only known of certain animals, and naturally cannot be applied to the human ovum without further proof.
The impregnated ovum is carried into the uterine cavity by the motive powers.already described. It finds the uterine cavity prepared for its re ception, in that its mucous membrane is markedly swollen and is disposed in folds. This swelling of the mucous membrane is considered by many (Reichert) to be nothing more than a continuance of the hypertemia oc casioned by the previous menstruation, but this is very improbable, since the impregnation has occurred some time after the menstruation, and in the intermediate time a subsidence of the swelling must have taken place.
It is much more probable that by the impregnation of an ovum, a renewed and intense congestion of the genitals is caused, which, in the short time necessary for the migration of the ovum into the uterine cavity, has already occasioned the swelling of the uterine mucous membrane and its disposal in folds. If the supposition that a portion of the mucous membrane is thrown off with each menstrual hemorrhage is true, and that a renewal of this portion is begun immediately after the hemorrhage, then the im pregnated ovum would implant itself in the regenerated mucous mem brane; then from the absence of ovulation, the exfoliation of the mucous membrane and the menstrual hemorrhage would not occur, and the decidual formation would proceed in the regular manner until toward the end of pregnancy, by its fatty degeneration, exfoliation and hemor rhage would again occur. Menstruation and parturition would then, to a certain degree, be identical processes. Let this be as it may, the im pregnated ovum is always arrested upon its emergence from the tube, by the swollen mucous membrane. The irritation which it causes ex cites an increased growth in the mucous membrane, so that it lifts itself around the ovum like a wall; this increased growth makes more rapid advances than does the growth of the ovum, so that the upper borders of this wall of mucous membrane unite over the ovum, and shut it off com pletely from the uterine cavity. The ovum then appears to be completely imbedded in the substance of the mucous membrane. The further pro cesses, which follow this implantation of the ovum, belong to another epoch of sexual life, pregnancy, which really begins with impregnation. But, since in the first few days of pregnancy, the discharge of the ovum is followed by no noteworthy disturbance, but is usually looked upon as a profuse menstrual flow, the condition of a woman, in whom these early abortions are constantly repeated, is almost the same as that of a sterile woman. And since the causes of these early abortions are usually the same as those which we recognize as the causes of sterility, we cannot interpose any objection from a practical standpoint if these early habitual abortions are looked upon as sterility.