90 HUMAN FECUNDITY 



the 59 cases mentioned above 12 per cent, were due to gonorrhoea. 

 Other diseases may cause sterility, such as tubercle and epididy- 

 mitis. Kelatively to the historical period as usually defined, 

 gonorrhoea is an old disease ; but we shall find reason for thinking 

 that the great majority of diseases have evolved since the time of 

 the pre-human ancestor, and to the extent to which this is true it 

 must be allowed that male sterility due to disease is more or less 

 recent. With these remarks we may leave the question of male 

 sterility, as it is relatively of little importance. 



3. It is therefore to factors which influence the female generative 

 process that we must look for the causes of such increase or 

 decrease of fecundity as are of importance. Certain factors may 

 be put aside on the grounds that there is no reason to think that 

 they have been of more importance at one time than at another. 

 Such are malformations of any kind that prevent the meeting of 

 the male and female gametes. 1 With regard to the factors of 

 importance it is by their influence upon different aspects of the 

 female generative process that they are best classified. There are 

 three main aspects of this process, variations in any of which will 

 influence fecundity. These are the length of the mature period, 

 the interval between births, and the number at a birth. 



Some reference to the nature of the female sexual cycle in 

 mammals has been made. The beginning of maturity is usually 

 measured by observing the beginning of menstruation. It is, 

 perhaps, worthy of mention that the beginning of menstruation 

 does not always coincide with the beginning of ovulation. Thus 

 the estimation of the duration of the mature period made by 

 watching for the beginning and end of menstruation is not always 

 exact ; the difference is not of consequence here, but the fact that 

 a difference is possible emphasizes that what is essential in the 

 whole process is ovulation. The true mature period is the period 

 during which ovulation occurs. The interval between births is 

 also dependent upon ovulation and so is number at a birth. 2 In 

 fact what we are asking is in the main what factors influence 

 ovulation. 



4. The information regarding the duration of the mature period 

 is not satisfactory. Though there is a large amount of information 

 about the beginning of menstruation, there is little information 



1 See Mosnier-Clauzel, De quelques Causes de Stirilitb chez la Femme, for a 

 summary of this question. a Except in the case of ' identical ' twins. 



