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 time of its exit until the succession of another ovulation, the woman is considered not liable to conception.

It is to be regretted, that, at the present state of physiological knowledge, the precise duration of the egg's sojourn cannot be ascertained. From two to fifteen days are the limits after which a woman is supposed not to be liable to conception; but even this rule has often been intruded upon, which renders the theory rather unreliable.

The fertilization of the egg often takes place two or three days before the expected menstrual flow, which is then interfered with and even suppressed by the very fact that conception has occurred. This proves that the process of ovulation may happen two or three days before the return of the menses, and that therefore the woman is liable to conception at that time. The process of ovulation and the exudation of the menses need not occur simultaneously.

During ovulation, we have already stated, there is a determination of blood to the ovaries, uterus, &c. This excess of blood seems necessary for the maturation of the egg, and to its final escape from the Graafian vesicle and the ovary. When this process is completed, the uterus, and other parts oppressed by this excess of blood, are relieved by an exudation of the superfluous matter from the womb: this it is which is called menstruation, or monthly flow. Should the ovum, however, become fecundated before menstruation takes place, that excess of blood would be needed for the formation of those membranes which are to envelop the fructified egg as it descends into the womb; and, consequently menstruation would not take place, or, if it did, it would be but scanty. Menstruation, therefore, is totally dependent upon ovulation, and affected by fecundation. To prove this further, cases are