REPRODUCTION IN MAN 1371 



tion. But there has been much division of opinion as to the exact 

 relation between the two processes. Fairly definite clinical and post- 

 mortem evidence has been brought forward for the theory that ovula- 

 tion precedes the menstrual flow. On this theory the degeneration of 

 the uterine mucous membrane, which occurs at each period, repre- 

 sents, so to speak, the undoing of a preparation for the reception of 

 a fertilised ovum. The ovum has been discharged, the mucous mem- 

 brane has been prepared for its reception, but fertilisation not having 

 taken place, ovum and mucous membrane are cast out together in 

 the menstrual flow. Unfortunately almost equally definite clinical 

 evidence has been adduced for the view that ovulation occurs during 

 or after the menstrual period. Light is thrown upon the question 

 by the study of the phenomena of ' rut ' or ' heat ' in the lower animals. 

 In most mammals impregnation and conception can only occur at 

 certain definite periods of the year. At these seasons the female 

 presents a swelling of the mucous membrane of the external genitals, 

 and often a flow of blood or mucus. As a rule it is only when in this 

 condition that it will permit the approach of the male. Thus the bitch 

 ' comes on heat ' as a rule twice in the year ; the cat three or four 

 times ; most carnivora only once a year. At these periods the uterus 

 shows well-marked histological changes, which may be divided into 

 the following periods : 



(1) The period of rest. During this time, which extends over the 

 greater part of the year, the mucous membrane is thin and pale. The 

 period of heat being known as the oestrus, this first period is denoted 

 by Heape the ana strum. 



(2) The period of growth or congestion. This corresponds to the 

 pre-menstrual thickening of the mucous membrane of the human 

 female. 



(3) Period of destruction, associated with haemorrhages into the 

 mucous membrane, desquamation of the superficial epithelial cells, 

 and occasionally discharge of blood and mucus from the vagina. 

 These two periods are grouped together as the pro-oestrum. 



(4) Period of recuperation corresponding to the post -menstrual 

 regeneration of the mucous membrane. It is during the first part 

 of this period or at the very end of the last period that ovulation occurs 

 in those animals where ovulation is independent of coitus. It is at 

 this time, too, that the animal exhibits sexual desire and permits the 

 approaches of the male. If fertilisation occurs, the mucous membrane 

 undergoes rapid hypertrophy, much more marked than that occurring 

 during the pro-osstrum. In the absence of impregnation the mucous 

 membrane returns to the condition of rest, the stage of return being 

 known as the met oestrum. 



These results have been found by Heape and Marshall to apply to 



