In the second place physiologists have en deavoured to argue respecting the place of fecundation from the well-known fact that, in the common fowl, turkey, and probably some other birds, a single connexion with the male serves to fecundate more than one ovum, as, for example, in the common fowl twelve or twenty ova; and that, as there is usually only one ovum in the progress of descent through the oviduct at one time, we must conclude either that the yolks or ovula are fecundated by the rise of the seminal fluid to the ovary, or that the seminal fluid remains somewhere in the course of the oviduct, to be applied to the ovum as it descends. If we exclude the notions of an aura and sympathetic action, the former of the above-mentioned views ap pears to us the most consistent with the facts that have already come under our knowledge. The notion entertained by Fabrieius and others that there is a receptacle for containing the seminal fluid in the oviduct appears to be in correct; and we find it difficult to believe that the seminal fluid can remain dispersed through the oviduct, or confined in any particular part of it and retain its power of fecundation, when we consider the manner in which each yolk descends from the ovary and receives in its passage the various accessory parts constituting the albumen and external coverings. Of course, in supposing fecundation to take place in the ovary, there remain two suppositions which may be entertained regarding the mode in which the seminal fluid gains the ovula ; for it might either pass directly up the tube of the oviduct, or be absorbed and take some cir cuitous course.
In the third place, we are inclined to think that in quadrupeds the ova must be already fecundated before their arrival in the uterus, that is, either in the neighbourhood of the ovary or in the tubes, for this reason, that at the time when the ovum first arrives in the uterus, it has already become considerably enlarged, and has undergone some of the changes of development;* and when we con sider how very regular and progressive these changes have been observed to be from the time when the ovum first enters the tubes, we shall be disposed to conclude that fecundation very probably takes place before then, or in the upper part of the tubes.
In the fourth place, attempts have been made to trace the seminal fluid in animals opened shortly after sexual union. Most authors agree that much of the seminal fluid frequently flows out of the vagina soon after coition, and Harvey, De Graaf, and Haller were all unable to discover any traces of seminal fluid in the uterus even of various animals killed and opened soon after sexual union. Haller, however, while he states this as the result of his experiments, admits that the means which he possessed of ascertaining the presence or absence of the semen were im perfect, and he himself believed that fluid to have entered the uterus.
Various other physiologists, also, state that they have found seminal fluid in different parts of the female organs. Morgagni and
Ituysch had two opportunities of examining the body of the human female very soon after coition, and found, on opening the uterus, a fluid which they regarded as semen. John Hunter states that he observed the same in a bitch, as also did Hausmann. But in all these instances some doubt may be enter tained regarding the fluid which was considered as semen.
Prevost and Dumas, trusting to the occur rence of the seminal animalculm as a certain sign of the presence of seminal fluid, state that they have observed these animalcules, at different periods after coition, both in the uterus and tubes of dogs and rabbits; and it appears to result from the careful series of experiments performed by these physiologists that the longer the time was which had elapsed after coition, the farther the seminal fluid had advanced upwards within the female genital passages. Thus, at twenty-four hours after coition a great quantity of animalcules were found in the comua of the uterus, but none either in the vagina or farther up the tubes; at forty-eight hours nearly the same was the case : on the third and fourth days there were many animalcule' still in the coroua and some in the tubes, which continued in the dog till the fifth and sixth days; and upon one occa sion only they observed a few animalcules near the infundibulum.
Burdach and others, again, are not inclined to place much reliance on these observations, because animalculx of the nature of Cercarir have been noticed in the genital passages of female animals which had had no connection with the male.
In the fifth place, experiments on the me chanical obstruction of the uterus, Fallopian tubes, and vagina, appear of considerable im portance in reference to this part of our sub ject. Experiments of this kind were per formed first by Haigbton,' and afterwards by Blundell ; the results of which, making allow ance for the more accurate knowledge we now possess respecting the indications afforded by the condition of the vesicles and corpora lutea in the ovary, may be stated as follows:— 1st. That when one of the eomua of the uterus or Fallopian tube of the rabbit is divided within a few hours after coition, and oblite ration of the tube has followed, although corpora lutea are formed in both the ovaries (as a consequence of the rupture of vesicles), ova are not to be found on the injured side of the uterus, but pregnancy takes place on the other side.
2d. When the vagina was divided in a like manner at its upper part, although the usual number of corpora lutea were found in the ovaries, pregnancy did not occur. That the mere wound itself locally, or its hurtful effects on the constitution, did not prevent the develop ment of the ova, was proved by the experiment purposely made of dividing the parts in the same way and allowing them to reunite by adhesion without obstruction of the tube, in which case uterine pregnancy occurred nearly as in the natural condition.