MECHANISM OF FECUNDATION. 893 



tion takes place at any definite time before, during, or after the menstrual period, nor 

 do we know precisely how long the spermatozoids may retain their vitality in the female 

 generative passages. 



The question of the duration of vitality of the spermatozoids after their passage into the 

 uterus has an important bearing upon the time when conception is most liable to follow 

 sexual intercourse. The alkaline mucus of the internal organs actually favors their move- 

 ments ; the movements are not arrested by contact with menstrual blood ; and, indeed, 

 when the spermatozoids are mixed with the uterine mucus, they simply change their 

 medium, and there is no reason to believe that they may not retain their vitality as well 

 as in the mucus of the vesiculse seminales. We cannot, therefore, fix any limit to the 

 vitality of these anatomical elements under physiological conditions ; and we cannot say 

 positively that spermatozoids may not remain in the Fallopian tubes and around the 

 ovary, when intercourse has taken place immediately after a menstrual period, until the 

 ovulation following. There is an idea, based upon rather general and indefinite obser- 

 vation, that conception is most liable to follow an intercourse which occurs soon after a 

 monthly period ; but it is certain that it may occur at any time. It is extremely probable 

 that, during the unusual sexual excitement which the female generally experiences after 

 a period, the action of the internal organs attending and following coitus presents the 

 most favorable conditions for the penetration of the fecundating elements, and this may 

 explain the more frequent occurrence of conception as a consequence of intercourse at 

 this time. 



'Mechanism, of Fecundation. -In considering the intimate mechanism of fecundation, 

 we may begin with the proposition that this is accomplished by an actual union with the 

 substance of the ovum of a greater or less number of spermatozoids. This fact, which 

 has long since been positively demonstrated by experiments, affords a material explana- 

 tion of hereditary transmission, not only of maternal, but of paternal physical and mental 

 qualities. 



There are many questions connected with hereditary transmission, which, if they 

 were susceptible of any thing approaching a positive scientific explanation, would be of 

 great interest and might appropriately be discussed in a work upon physiology; hut. 

 although the facts of hereditary influence, as regards the inheritance both of physiologi- 

 cal and morbid attributes and tendencies, the influence of the maternal mind upon the 

 development of the foetus, the effects of previous pregnancies, etc., cannot be doubted, 

 their consideration would involve little more than a mere enumeration of remarkable 

 phenomena. 



The first question which naturally arises, and which has engaged the attention of 

 ancient as well as modern authors, relates to the conditions which determine the sex of 

 the offspring. The older writers, whose exact physiological knowledge was compara- 

 tively limited, were able to present explanations of some of the phenomena of generation, 

 which were more or less satisfactory in their day ; but many of these have been contra- 

 dicted by more recent facts, which have only rendered the causes of the phenomena more 

 obscure. Iconoclasm in physiology is almost a necessary consequence of the requisition 

 of definite knowledge ; and too often the exact student must fail to substitute anything 

 to supply the places of the broken images of antiquity. This is illustrated in the ./ 

 tion of the determination of the sex of offspring. Statistics show clearly enough the 

 proportions between male and female births; but nothing has ever been done in the 

 of procreating male or female children at will. According to Longet. the proportion of 

 male to female births is about 104 to 105, these figures presenting certain nioditiea' 

 under varying conditions of climate, season, nutrition, etc. It has been shown, by \ 

 extensive observations upon certain of the inferior animals, that the preponder.-u. 

 in births bears a certain degree of relation to the vigor and age of the parent*: and that 

 old and feeble females fecundated by young and vigorous males bring forth a gre. 



