In order, therefore, to determine as nearly as possible the precise limits of the functions of the oviducts, it will be necessary to ex amine more particularly the evidence, which serves to show, that while the ovary is the part in which the ovum is formed, and the uterus that in which it is developed ; the Fallopian tube, besides being the conductor of the ovum from the formative to the reci pient organ, is also the seat of the second most important step in the process of genera tion, namely, its fertilisation.
Here human physiology is so much at fault that it a.ain becomes necessary to resort to the evidence furnished by experiments, and observations made upon the maim-1mila ge nerally.
Now, one of the most remarkable circum stances relating to the generative process in the mammalia is, that the periods of separa tion of the ova from the ovary, and of' their passage down the Fallopian tube, are coinci dent with the cestrus. Bischoff, indeed, has ascertained, in the bitch, that by the time the ovum has reached the uterus, or even the lower end of the oviduct, the period of heat, or desire for sexual coneress, has passed away, and consequently the opportunity for impregnation is lost. In the Guinea-pig also it appears certain that the opportunity for impregnation is already gone by the time the ovum has quitted the tube, and has reached the uterus ; for the ostrus is then long passed, the coitus has long ceased to be permitted, and even the vulva is at this time again contracted. And although doubtless these conditions vary in different genera, yet a variety of circumstances, of which a more particular account will be presently given, renders it probable that the rule is general among the niammalia, that insemination shall occur coincidently with the passage of the ovum down the Fallopian tube.
Next, it may be shown, by the experiments of Cruikshank, Haighton, Blundell, and Bischoff, which consisted in deligation or excision of portions of the tube, that when ever the obliteration of the canal was com plete, and had been effected prior to the act of copulation, fertilisation of the ovum was rendered hnpossible.
These experiments were most satisfactory when performed on one side only of the ge nerative organs, so as to leave free play for the natural functions of the other ; and thus the negative results obtained on the one half of the body being set off against the positive ones of the other, served to enhance the value of both. By such experiments it may be shown.that mechanical obstruction of the tube, while interfering in no respect with the spontaneous separation of the ovum from the ovary, or its reception by the mouth of the tube, and descent as far as the seat of ob struction (provided indeed that care is taken in the experiment not to destroy the vascular supply of the parts), prevents the completion of the reproductive act, and stops it at this stage, by impeding the access of the sper matic fluid to the ovum.
But the results of such experiments will necessarily vary according to the time and place of application of the ligature. Thus while division or deligation of the tube before, or even very shortly after, intercourse pre vents impregnation of the ova, yet, according to Haighton, the same experiment performed sixty hours after coitus had no effect what ever in impeding the development of the em bryo, for in that time the encounter of the generative elements would have already taken place.
But although these experiments may be infinitely varied, they cannot afford such sa tisfactory information as may be derived from the actual examination of the contents of the tube where natural impregnation has been allowed to obtain, especially when these exa minations have been conducted with the aid of the microscope. In this way inay be ob tained an amount of collective evidence that leaves little to be desired for the purpose of fully elucidating the history of the ovum dur ing that brief but important period which intervenes between its quitting the ovary and its entrance into the uterus. But since an account of the development of the ovum does not come within the scope of this article, only so much of the subject will be given here as will be requisite to continue the ar gument for the purpose of showing what is the precise part which the Fallopian tube takes in the process of impregnation.
There can be no question that the mam malian ovum, after an efficient coitus, enters the uterus in a condition differing in many important particulars from that in which it ordinarily quits the ovary. And although a certain amount of variation is perceptible in regard to the actual changes experienced by the ovum in different species, during its pas sage through the tube, yet so constantly are the main features preserved, that the obser vations made upon any one species will ge nerally. serve as a type of the rest, and cer tainly the aggregate of these observations, agreeing closely as they do with one another, render the conclusion in the highest degree probable, that changes not very different from these occur also in the ovum in man.