3d. In another set of experiments oblite ration of the tubes was caused to take place at a later period, probably when the ova had descended and may he supposed to have met with the seminal fluid, and in these animals pregnancy occasionally but not always oc curred.
It would appear to follow from these expe riments, that the seminal fluid does not rise in the female genital passages immediately upon its introduction, and not for more than a day after coition, and that those circumstances which impede the rise of the seminal fluid prevent fecundation. But they do not warrant the conclusion that impregnation must occur in the ovaries, since the vesicles may have burst, their contents be discharged, and corpora lutea formed without the seminal fluid having had access to the ovary; a fact which is well shewn by the interesting experiment performed by Dr. Blundell, of producing an obliteration of the upper part of the vagina in the unim pregnated rabbit, then allowing coition to take place, and then finding, no pregnancy, but corpora lutea in the burst vesicles of the ovary.
These experiments appear also as of im portance in shewing that neither absorption of the semen by the lymphatics or bloodvessels, nor the passage by any other circuitous route, nor indeed any sympathetic action established by sexual union between remote parts of the female generative organs, can be the means of producing fecundation.
There are, no doubt, great difficulties in the way of our understanding by what manner the seminal fluid accomplishes the passage up wards in the genital organs of the female. Thus, the small size of the Fallopian tubes at once strikes us as a powerful obstacle ; but in many animals, as, for example, in the Rumi nantia, there is an equally great difficulty in comprehending how the seminal fluid gains the uterus itself even ; for in these animals the os uteri forms a long and uneven passage, inter rupted by many hard cartilaginous projections, and closed in general by a very viscid and tena cious mucus. But yet the seminal fluid must in all probability enter the cavity of the uterus.* In conclusion, we would remark that we must either suppose fecundation to be the effect of the actual contact of the seminal fluid with the ova in the upper part of the Fallopian tube or somewhere near the ovary, or we are reduced to form the opinion that the action of the seminal fluid on the lower part of the female genital organs may be twofold, viz. first, causing the commencement of the process of fecundation by a sympathetic in fluence on the upper part of the tubes, and, in the second place, perfecting the change in the uterus when it meets there with the ovum.
We feel inclined, in the present state of our knowledge, to give a preference to the first of these opinions.
Nature of the ,fecundating process. Hypo thesis of an aura, 4.c.—We return now to the consideration of the essential nature of the change of fecundation.
The opinion that fecundation is attributable to the agency of an aura or emanation from, and not to the material contact of the seminal fluid, is founded chiefly upon alleged instances of conception having occurred in individuals (of the human species) in whom, from unnatural formation or disease, no direct passage existed from the vagina or external aperture to the internal organs, as well as upon some of the circumstances above alluded to, as shewing the difficulty of such a passage both in man and animals, even in the natural condition.
No very definite idea, it may be remarked, can be attached to the term " aura," for it has been employed in varous acceptations by diffe rent authors ; one considering it as of the nature of a gaseous or vaporific exhalation from the seminal fluid, another denying it the nature of a substance even of the most etherial kind, and considering it more as a spiritual or vital principle ; and a third regarding it as of the nature of a nervous impression. These discrepancies only spew us that the term aura is to he taken rather as an expression for the unknown agency of the seminal fluid which causes fecundation, than as indicating its modus operandi or the part of its substance more immediately concerned in the action. Some authors have, however, even referred to direct experiment in favour of the agency of an aura. Mondat, for example, (De la Sterilite, 4to. edition, p. 17) states that he witnessed experi ments performed by Morsaqui, of Turin, with this view, from which it was found that the bitch could be impregnated when it was im possible, as he states, that the substance of the seminal fluid could in substance pass into the uterus or other parts. Recurved tubes, con taining in the closed end a quantity of the dog's seminal fluid, were introduced into the vagina of the hitch in such a way that none of the fluid itself could escape, but only an emanation, vapour, or supposed aura rising from it, and in eighteen out of thirty animals on which the experiment was performed, with the subsequent occurrence of impregnation. But until these experiments shall have been confirmed by careful and frequent repetition, we must be allowed to doubt the possibility of performing such an experiment in a sufficiently accurate manner.