506 PLAIN FACTS FOR OLD AND YOUNG 



... If, on the other hand, coitus does not take place, 

 the egg passes down into the uterus unimpregnated, 

 loses its vitality after a short time, and is finally car- 

 ried away with the uterine secretions." 



''It is easily understood, therefore, why sexual in- 

 tercourse should be more liable to be followed by preg- 

 nancy when it occurs about the menstrual epoch than 

 at other times. . , . Before its discharge, the egg is 

 immature, and unprepared for impregnation ; and after 

 the menstrual period has passed, it gradually loses its 

 freshness and vitality." 



The law of periodicity, as it affects the sexual ac- 

 tivity of males of the human species, is indicated in 

 the following remarks by the same author: 



''The same correspondence between the periods of 

 sexual excitement in the male and female, is visible in 

 many of the animals [higher mammals], as well as in 

 fish and reptiles. This is the case in most species which 

 produce young but once a year, and at a fixed period, 

 as the deer and the wild hog. In other species, on the 

 contrary, such as the dog, the rabbit, the guinea-pig, 

 etc., where several broods of young are produced dur- 

 ing the year, or where, as in the human subject, the 

 generative epochs of the female recur at short inter- 

 vals, so that the particular period of impregnation is 

 comparatively indefinite, the generative apparatus of 

 the male is almost always in a state of full develop- 

 ment, and is excited to action at particular periods, 

 apparently by some influence derived from the condi- 

 tion of the female." 



Summary of Important Facts. —The facts pre- 

 sented in the foregoing quotations from Dr. Dalton 

 may be summarized as follows : 



1. The sexual function is for the purpose of pro- 



