v GENEEATIVE SYSTEM OF THE FEMALE 181 



account for the periodicity of the process he puts forward a 

 stimulation of the nervous centres by the progressive intu- 

 mescence and development of the follicle, and a reflex congestion 

 of the uterus and ovary. This congestion gives rise in the 

 uterus to the menstrual haemorrhage, and in the ovaries to a 

 more rapid increase in size and bursting of the follicle. 



The other theory taught by His and by his precursors and 

 successors considers likewise the periodic process of the uterus 

 as directed to prepare for the fertilised ovum a suitable bed 

 for striking root and for development ; but holds that this pre- 

 paration is represented by the tumefaction and congestion of the 

 uterine mucosa which precedes the haemorrhage, and to which is 

 due the formation of the catamenial decidua. If the ovum which 

 arrives in the uterus during this stage of the process is not 

 fertilised, it does not attach itself there but is lost through the 

 vaginal canal, and then follow the detachment of the decidual 

 epithelium and the menstrual haemorrhage. If, on the other 

 hand, the ovum has been fertilised, it inserts itself into the tume- 

 fied mucous membrane, which is a bed adapted for its reception 

 and development, and the haemorrhagic process does not take 

 place. According to this doctrine, then, menstruation is the sign 

 of a missed pregnancy, which would date not from the last 

 menstruation, but from the first which failed to occur. 



To this theory the objection may be raised that it is difficult 

 to understand how the fertilised ovum, directly it has become 

 adherent to the uterus, can exercise an influence so great as to 

 suspend the process in course and prevent the menstrual haemor- 

 rhage. It is known, however, that in some cases, although rare, 

 menstruation may continue even during pregnancy, specially in 

 the first month of gestation. Statistics collected by Hasler 

 (1876) of 248 cases of pregnancy, in which the day of the fruitful 

 coitus was well authenticated, show that conception most fre- 

 quently (in 86 per cent) takes place within the first ten days 

 from the cessation of menstruation. This is apparently evidence 

 in favour of Pfl tiger's theory ; nevertheless, this is not the theory 

 preferred to-day by obstetricians and gynaecologists, who show 

 little faith in the statistics of Hasler. 



IV. The organs of sexual copulation (coitus) are represented 

 in woman by the vagina and the vulva or pudenda. They serve 

 also to give exit externally to the periodic menstrual flow, and 

 in parturition to the product of conception. 



The vagina is a muscular caual, flattened when in its natural 

 state, from which it follows that when seen in section it presents 

 itself as a transverse fissure which at its extremities divides into 

 two branches so as to form the letter H (Fig. 65). When the 

 vaginal canal is distended, as occurs during copulation, or 

 the introduction of a speculum, it assumes the form of a hollow 



VOL. v N 2 



