MENSTRUATION 365 



The following considerations are also important in establishing the age of young 

 embryos. The time required for spermatozoa to travel to the upper end of the tube, 

 where fertilization takes place, is probably about twenty-four hours. There they 

 may fertilize the ovum at once if ovulation has just occurred. They retain their 

 vitality and are capable of fertilizing the ovum during a period of ten days in the 

 rabbit, and this may be true also of man. Thus it is probable that if coitus has occurred 

 shortly before menstruation, the spermatozoa may remain active in the tube, and 

 fertilize the ovum discharged at the close of the following menstruation. 



THE DISCOVERY OF MAMMALIAN OVA. 



During the seventeenth century the ovary was called the testis muliebris, or testis 

 foemineus. It was believed to produce the mucoid secretion which escapes from the 

 genital orifice, and this was regarded as seminal fluid. The uterine tubes were accord- 

 ingly the vasa deferentia mulierum, serving to convey this fluid to the uterus, where, 

 through a mixture and interaction of the male and female semina, an embryo was 

 produced. Aristotle had argued to the contrary, but his opinion was summarily dis- 

 posed of by Bartholin, who discussed the ovaries as follows (Anatomia, 1666): 



"Their function is to produce semen in their own way, which Aristotle, against all 

 reason and observation, has dared to deny to women, contrary to the express teaching 

 of Hippocrates. " 



The ancient doctrine of Aristotle, expounded in his treatise on the generation of 

 animals, was based upon the familiar facts that menstruation marks the beginning, 

 and ceases at the end, of the child-bearing period; and moreover menstruation is 

 interrupted while the embryo is being formed. Therefore he concluded that the men- 

 struum supplies the substance and material for the new body, which arises like the 

 curd in milk, through the agency of the semen. The semen engenders; the menstruum 

 nourishes. The theory had already been advanced that the semen comes from all 

 parts of the body, and that its particles reproduce the structures from which they are 

 derived. This enticing speculation, revived by Darwin in his theory of pangenesis, 

 was discussed at length and rejected by Aristotle. 



Generation, therefore, was considered to result from the mixing of two fluids, and 

 would have remained a barren physico-chemical problem until recent times, if further 

 morphological observations had not been made. The view of Bartholin had at least 

 the merit of definitely associating the ovary with the reproductive function. Vesalius 

 and Fallopius had seen the follicles and corpora lutea; Fallopius described them as 

 "vesicles filled with water or aqueous humor, some limpid and others yellow (Observa- 

 tiones, 1588). Many others had observed them, and from their resemblance to the 

 ova of birds they had even been called "ova," when in 1672 a young Dutch physician, 

 Regnerus de Graaf , made his thorough study of the female genital tract. 



De Graaf concluded that the "semen muliebre" is not produced by the "testes 

 muliebres," but that the general function of the latter is "to produce and nourish 

 ova, and bring them to maturity." Consequently he proposed to substitute the name 

 ovary, and to call the tubes oviducts. He declared that the ova escaped from the 

 follicles through minute apertures (in the rabbit admitting a bristle) and made their 

 way through the tubes to the uterus, in which they developed. The abnormal forma- 

 tion of a human embryo within the tube was figured and, to a certain extent, explained. 

 De Graaf studied many mammals, and especially rabbits* He found minute ova in 

 the oviducts and observed the follicles from which they had escaped. In older stages 

 he recorded a general agreement between the number of corpora lutea and embryos. 



