CHAPTER I. 



IMPREGNATION. 



SEC. 1. MENSTRUATION. 



687. FKOM puberty, which may be said to occur at from 

 13 to 17 years of age, to the climacteric, which may be said 

 to arrive at from 45 to 50 years of age, the exact time in each 

 case varying considerably and being apparently determined by 

 various conditions, the human female is subjected monthly to a 

 discharge from the vagina known as the l menses,' 4 catamenia,' 

 and by many other terms. The discharge is the result of 

 changes in the lining membrane of the uterus. A similar 

 change in the uterus occurs in the lower animals, being repeated 

 at intervals differing in length in different animals, and is 

 usually accompanied by sexual excitement and changes in the 

 external genital organs ; the phenomena are then spoken of by 

 such names as 4 heat,' ' rut,' &c. 



The female human, and other, is also subject to another 

 recurring process, the escape of an ovum from its Graafian 

 follicle in the ovary, a process spoken of as " ovulation." The 

 changes of the uterus during menstruation have the appearance 

 of being a preparation for the reception of a discharged ovum 

 so that the latter if fertilized may be developed into an embryo ; 

 and there are many reasons for thinking that the acts of ovula- 

 tion and menstruation are coincident with a causal connection 

 between the two. But this cannot be regarded as definitely 

 proved, and many observers maintain that menstruation may 

 and does occur without any discharge of an ovum, and con- 

 versely that an ovum may be discharged, as in copulation, quite 

 apart from menstruation. 



The discharge of an ovum, whether at menstruation, or at 

 another time appears to take place as follows. The whole 

 ovary at this time becomes congested, the blood vessels being so 

 dilated and filled with blood that we may almost speak of the 



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