REPB OD UCTION. 899 



scion is set, or, in uniting two membrane-covered tissues, the surgeon first wounds 

 or freshens their surfaces. The mechanism of this uterine process is as fol- 

 lows : The constant growth of the ovarian cells and the consequent swelling of 

 the ovary subject the ovarian nerve-fibres, and through them the spinal cord, 

 to a constant slight stimulation. Through the summation of the stimuli within 

 the cord a reflex dilatation of the vessels in the genital organs is produced. 

 The excessive blood-supply leads in turn to the tumefaction of the uterus, and 

 frequently to the ripening of a Graafian follicle. The bleeding follows, and 

 at the same time or slightly later the rupture of the follicle occurs, provided 

 the latter be sufficiently advanced in growth. The menstrual flow and ovulation 

 are, therefore, two phenomena conditioned usually by the same cause, namely, 

 the menstrual congestion, yet either may occur without the other. Pfliiger's 

 hypothesis accounts clearly for the absence of menstruation after removal of 

 the ovaries. Numerous other theories have been proposed, no one of which 

 can be said to be widely and generally accepted. The present tendency in 

 belief is as follows : Ovulation and menstruation are in great part independent 

 phenomena ; they may or they may not coexist ; the uterine growth is a prep- 

 aration for the future embryo ; the tissue of the decidua menstrualis is the fore- 

 runner of the decidua graviditatis (p. 909) ; if an ovum, whenever it is discharged, 

 be fertilized, it attaches itself to the thickened uterine wall, the tissues become 

 the decidua graviditatis, pregnancy follows, and the decidua is not discharged 

 until the time of parturition ; if, however, fertilization does not take place, 

 there is no attachment, the tissues degenerate and become the decidua men- 

 strualis, and the flow occurs. The suggestion of Jacobi l is not an extreme 

 one : " The menstrual crisis is the physiological homologue of parturition." 

 Its monthly periodicity is not explained. Regarding its mechanism the above 

 hypothesis of Pfliiger, although not yet proven experimentally, seems not 

 unreasonable. 



The mystery of menstruation largely ceases when we recognize what is un- 

 doubtedly a fact, that the phenomenon is a highly developed inheritance from 

 our mammalian ancestors, and that, although in the human race under the 

 influence of civilization and social life it has largely lost its technical sexual 

 significance, it is, nevertheless, primarily a reproductive phenomenon derived 

 directly from the lower females. Nature has endowed the latter, in a manner 

 yet unknown, with reproductive periods that are pronounced in the wild state 

 and are coincident with certain of the seasons. A primitive seasonal period 

 may perhaps still be shown in woman by the greater proportion of births that 

 take place during the winter months than at other times of the year : this sig- 

 nifies greater sexual activity during the months of spring, as is the case in 

 most animals. 2 



1 Mary Putnam Jacobi : American Journal of Obstetrics, xviii., 1885. 



2 " The largest number [of human births] almost always falls in the month of February, 



.... corresponding to conceptions in May and June Observations tend to show the largest 



number of conceptions in Sweden falling in June ; in Holland and France, in May-June ; in 

 Spain, Austria, and Italy, in May ; in Greece, in April. That is, the farther south the earlier 

 the spring and the earlier the conceptions." Mayo-Smith : Statistics and Sociology, 1895. 



