MENSTRUATION. 459 



At the commencement of a period, the menstrual discharge 

 is viscous, consisting largely of mucus from the uterine glands, 

 slightly tinged with blood ; in the middle of the period the flow- 

 becomes almost pure blood ; while towards the end it becomes 

 paler, the mucus again preponderating. Owing to mixture with 

 the uterine mucus, the blood of the menstrual flow does not coagu- 

 late. The total amount of the menstrual discharge is usually 

 from four to six ounces ; but this may be widely departed from 

 in individual cases, either in the way of diminution or of excess. 



On the cessation of the menstrual flow, the uterine epithelium 

 is very quickly regenerated, spreading over the surface from the 

 pecks of the uterine glands. It is completely reformed within 

 three or four days of the end of the menstrual period. After 

 this re-establishment of the uterine mucous membrane, the 

 uterus remains in a quiescent condition for from ten days' to a 

 fortnight ; at the end of this time it begins to swell again, and 

 the menstrual process is repeated. This repetition occurs, as 

 already noticed, at intervals, usually of four weeks, throughout 

 the whole child-bearing period ; the only normal disturbing 

 element being gestation, during which menstruation is in 

 abeyance, recommencing a short time after the birth of the child. 



5. E xplanation of the Menstrual Process. . 



The complete menstrual cycle, occupying in typical cases 

 twenty-eight days, may be divided into four stages, which 

 follow one another in regular sequence. 



(i) The first or constructive stage is characterised by swelling 

 of the mucous membrane, enlargement of the uterine glands, 

 and increase in the connective-tissue cells of the mucous mem- 

 brane ; it results in the formation of a menstrual decidua, lining 

 the entire uterus. 



(ii) The second or destructive stage includes what is ordinarily 

 known as the menstrual or catamenial period. It is marked by 

 abundant discharge of mucus from the enlarged glands, and by 

 the disintegration and discharge from the uterus of the inner 

 layer of the mucous membrane. It involves loss of the epithelial 

 lining of the uterus and of the necks of the- glands, and is accom- 

 panied by haemorrhage. 



(iii) The stage of repair comes next, during which the 

 uterus is recovering from the destructive changes. The uterine 



