66 THE PHYSIOLOGY OF REPRODUCTION 



and Greenland menstruate less frequently, whereas in certain 

 low and hot countries the catamenia may recur every three 

 weeks. 1 



Further, the regularity with which the menstrual periods 

 occur is liable to be disturbed by environmental changes. Thus, 

 it is stated that change of residence, or foreign travel, without 

 otherwise affecting the health, may bring about amenorrhoea or 

 a temporary cessation of menstruation. 2 Such an effect is, no 

 doubt, comparable to the well-known influence of captivity or 

 change of environment in arresting the sexual functions of 

 many animals. 



The commonest time for the continuance of the menstrual 

 flow is said to be about three or four days in this country, but 

 it may last for as long as eight days, or, on the other hand, for 

 only a few hours without disturbance of health. It usually 

 begins gradually, becoming most profuse about the second or 

 third day, and then diminishes. 3 The total amount of blood 

 lost has been variously estimated at from two to four ounces. 

 In hot climates the quantity is greater than in cold ; and it is 

 said to be increased by luxurious living, and also by abnormal 

 mental stimulation. The character of the menstrual discharge 

 and its source of origin can best be considered in describing the 

 histology of the uterus during the cestrous and menstrual cycles 

 (see Chapter III.). 



The monthly development of the uterine mucous membrane 

 which precedes the menstrual discharge is often accompanied 

 by a fulness of the breasts which begins to disappear after the 

 commencement of the flow. Swelling of the thyroid and 

 parotid glands, and tonsils, as well as congestion of the skin 

 and a tendency towards the formation of pigment, are also 



1 Matthews Duncan, "Sterility in Women," Brit. Med. Jour., 1883 ; and 

 Lay cock, loc. cit. 



2 Wiltshire, loc. cit. 



3 Galabin, A Manual of Midwifery, 6th Edition, London, 1904. The age 

 at which menstruation begins varies in different countries, being earlier in 

 warm climates than in cold ones. In our own country the first menstrua- 

 tion does not usually occur before the age of fourteen or fifteen, while the 

 menopause (or period when menstruation ceases) begins about the age of 

 forty-five. (See p. (572.) Kennedy (Ed in. Med. Jour., vol. xxvii., 1882), how- 

 ever, has reported a case of a woman who continued to menstruate after 

 giving birth to a child at the age of sixty-three. 



