60 THE PHYSIOLOGY OF REPRODUCTION 



part of the tropical lunar period than at other parts. The inference 

 drawn is that the moon's declination may have been one factor 

 among a number that determine the time of menstruation. Such 

 a conclusion, however, must be accepted with great reservation 

 seeing that the dioestrous cycle in the lower Mammals may be three 

 weeks or fifteen days, or some other period having no relation to 

 lunar periodicity. 



It is stated, also, that the periodicity of menstruation depends 

 partly on the climatic conditions, and that women in Lapland 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 amenorrhoaa 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 oastrous and menstrual cycles 

 (see Chapter III.). 



The monthly development of the uterine mucous membrane 

 which precedes the menstrual discharge is often accompanied by a 

 fullness of the breasts which begins to disappear after the commence- 

 ment of the flow. Swelling oi' the thyroid and parotid glands, and 

 tonsils, as well as congestion of the skin and a tendency towards the 



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

 Laycock, loc. cit. 



2 Wiltshire, loc. cit. 



3 Galabin, .1 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 menstruation 

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

 pause (or period when menstruation ceases) begins about the age of forty-five. 

 (See p. 715.) Kennedy (Edin. Med. Jour., vol. xxvii., 1882), however, has 

 reported a case of a woman who continued to menstruate after giving birth 

 to a child at the age of sixty-three. 



