Thus, if even the foregoing explanation coultl be deemed satisfactory, it appears ne cessary occasionally to fall back upon the old doctrine of the detachment of ova coincidently with fecundation, in order to supply the de ficiencies of the newer theory of their sponta neous etnission independently of it. It must however be confessed, that every view yet offered of the direct dependence of each sepa rate act of menstruation upon a corresponding act of ovulation, disappoints expectation by leaving some condition relating to conception unexplained, or explainable only by raising an additional hypothesis ; while many circum stances of common occurrence, such as the sudden reappearance of menstruation under mental emotion and the like, are left unac counted for upon any hypothesis of ovarian doininance.
If next the ovular view of menstruation be tested by the evidence derived from anatomy, although many facts will be found in proof of the statement that ova are often emitted at the menstrual period, these cases have not been yet sufficiently collated to form a series capable of affording unquestionable conclusions as to the precise relation which the emission of ova bears to each menstrual act. That ova may pass spontaneously from the ovary during the menstrual flow is proved by cases already' given at p. 567. and 605. NI. Pouchet, however, supposes that it is the maturation of the ova which takes place during menstruation, and that their emission f011ows immediately or within four days after the cessation of the flow. AI. Coste found the period of rupture of the Graafian follicle to be very variable. In one case the follicle was already burst on the first day of menstruation. In a second in stance, although five days had passed from the cessation of the flux, the follicle was still entire, though the slightest pressure sufficed to cause its rupture. In a third casefifteen days had elapsed, and yet rupture had not taken place. In the example represented by fig. 380. ten days had passed since the last men struation began, and the follicle was entire, though perfectly ripe, and apparently upon the point of rupture.
These examples, in the same degree that they favour a belief in the occurrence of im pregnation at indefinite periods of the men strual intervals, by showing how conception is then possible, discourage the view that the emission of ova is necessarily limited to the precise times of the menstrual flow. But until a larger number of examples than yet exists, showing the condition of the follicles during both the menstrual periods and inter vals, has been collected and carefully com pared, no definite conclusions as to the exact relation which the emission of ova bears to each act of menstruation can be arrived at, so far as anatomical evidence is concerned.
For the attention of observers having been directed more to the condition of the ovaries at the time of menstruation than in the inter val, much inore has been ascertained of their state at the former than at the latter periods. Yet it is during the intervals of menstruation that conception in man normally takes place, while mammals become impreg,nated only during the testrus.
It is important, therefore, to determine, thirdly, how far the cestrus or rut in the mam malia ntay be regarded as comparable with the act of menstruation in the human female; for if, as is commonly supposed, these two functions are identical, or nearly so, then the facts to be derived from comparative anatomy may assist further in determining the nature and extent of the relation between menstruation and ovu lation in man. But if the phenomena atten dant upon the rut do not, in all respects, coin cide with those accoinpanying nienstruation, the conclusions which are legitimately de ducible from observation of the former func tion must not be too strictly applied to the latter.
In the manimalia the periods of emission of the ova from the ovary, and of their passage down the Fallopian tube, are undoubtedly coincident with the cestrus. It is only on these occasions that the female manifests an instinc tive desire for copulation. She is then said to be in heat. The vulva is congested, swollen, and bedewed with an increased secretion, which is generally odorous, and is sometimes tinged with blood. This condition is of brief duration. At the longest it continues for a few days. But whatever be its duration it is the only period during which the female can be impregnated.
In the human subject the periodical return of congestion of the reproductive organs, the rnenstrual flow, and the corresponding spon taneous emission of ova, so far as this point has yet been ascertained by post-mortem ex amination, accord with the phenomena dis played by the mammalia during the cestrus. It is also believed that in somc instances concep tion has taken place during menstruation*, a circumstance which is clearly reconcilable with the anatomical evidences already- produced, and is so far in accordance with what nor mally occurs in the mammalia during cestrua tion.