The attempt to determine this point in the human subject has generally proceeded upon a comparison of the condition of early ova found in the uterus, or prematurely expelled from it, with the last known date of inter course or of menstruation ; but neither of these modes of calculation can afford any certain information : for it is obvious that the first can give no more than the date of insemination (as, for example, when a single intercourse has occurred), but will throw no light upon the question of the time which may have elapsed since the ovum quitted the ovary, and how long it may have re mained unimpregnated in the tube ; while the second mode is rendered equally uncer tain for want of more precise knowledge than we at present possess of the actual relation in point of time between menstruation and ovulation. See p. 669.
The analogies which other mammalia fur nish justify, to a certain extent, the suppo sition, that the time occupied by the passage of the ovum through the tube in rnan is not materially different. But the circumstance that, in man, the periods of capacity for impregnation are not restricted to definite occasions, to the same extent that they are in brutes, greatly diminishes the value of any calculations which might be based upon these analogies.
We may next examine the evidence by which it may- be shown that the Fallopian tube serves, on the other hand, as a conduit for the spermatic fluid towards the ovary. That it performs this office, in addition to that of conveying the ova downwards into the uterus, is abundantly proved by the direct observations of Prevost and Dumas, Bischoff, Barry, Wagner, and many others ; whose experiments serve to show, also, to what extent the spermatozoa are capable of pene trating within the tube, and of retaining their power of motion there.
Bischoff, after repeatedly finding sperma tozoa in active movement in the vagina, and particularly in the Fallopian tube of the bitch, though in this latter situation the movements had ceased, was so fortunate as to trace them in an animal that had been Jined on two successive days, and was killed half an hour after the last coitus, not only in the uterus, but also in active tnotion through the whole length of the tubes, and between the fimbrim, and finally in the sac or cap sule which the peritoneum forms around the ovary, and even upon the ovary itself. Wag ner also found in a bitch, killed forty-eight hours after coitus, spermatozoa motionless in the vagina but active in the uterus, in whose cornua, as well as in the Fallopian tubes, their number and activity conspicuously in creased as far as the abdominal extremity, where they completely filled every fold of membrane, and were seen moving among the fimbrix, but none were found in the capsule or pouch that surrounds the ovary. By
Barry the same fact of the possibility of the spermatozoa penetrating to the utmost ex tremity of the tube, and even as far as the surface of the ovary, has been demonstrated. Of the latter he gives two instances ; but that the seminal fluid does not commonly penetrate so far as the ovary may be inferred froni the statements of Prevost and Dumas, who could never find them in this situation, and of Barry, who, acknowledging the ac curacy of those observers, says himself, that in seventeen out of nineteen instances in the rabbit, he was unable to detect the spermatic fluid upon the ovary, and in one of the two cases in which he had observed it there, the only evidence of the fact was the presence of a single sperrnatozoon.
By no observer, so far as I am aware, have spermatozoa ever been detected within the ovary of any mammal.
The rapidity with which the spermatic fluid is capable of reaching and entering the tube is sometimes very considerable. Bischoff has observed spermatozoa within the oviduct of the Guinea-pig immediately after the coitus; in one instance, indeed, he traced them as far as the middle of the tube, in little more than three quarters of an hour after that event, though it had been commonly supposed that a period of nine or ten hours was requisite for the penetration of spermatozoa to the ex tremity of the tube.
The power by which the semen reaches the oviduct is partly the act of ejaculation, which may suffice to carry it to the end of the uterus, partly the peristaltic action of the uterus and tubes, in those animals in which these parts have flexible walls; partly, also, the movements of the spermatozoa themselves. But the cilia lining the tubes can in no way contribute to this effect, since their action would create a current in the contrary direc tion to the ascent of the fluid.
Thus it has been shown that the Fallopian tube, or oviduct, performs the double office of conveying the ova from the ovary towards the uterus, and of serving as a conduit for the passage of the spermatic fluid from the uterus towards the ovary ; and the conclusion is almost inevitable, that, by these combined operations, the encounter of the generative elenients will most probably take place at some point within the tubal canal. It may, however, be objected, that since the sper matic fluid has been known occasionally to reach as far as the ovary, impregnation may occur there; or, on the other hand, that inas much as this fluid must necessarily, in part at least, fill the uterus before it can occupy the oviduct, the ovum may not become impreg nated until after it has reached the principal cavity of the generative track.