DEVELOPMENT OP THE EMBRYO. 



1015 



counted for by the fact, which is one of the most remarkable contributions that 

 have yet been made by Statistics to Physiology, that the Sex of the offspring is 

 influenced by the relative ages of the parents. The following table expresses 

 the average results obtained by M. Hofacker 1 in Germany, and by Mr. Sadler 3 

 in Britain ; between which it will be seen that there is a manifest correspond- 

 ence, although both were drawn from a too limited series of observations. 

 The numbers indicate the proportion of Male births to 100 Females, under the 

 several conditions mentioned in the first column. 



Father younger than Mother 

 Father and Mother of equal age 

 Father older by 1 to 6 years 

 " " 6 to 9 

 " " 9 to 18 

 " " 18 and more 



Hofacker. 



90.6 



90.0 



103.4 



124.7 



143.7 



200.0 



Father younger than Mother 

 Father and Mother of equal age 

 Father older by 1 to 6 years 



6 to 11 

 11 to 16 

 " " 16 and more 



Sadler. 



86.5 



94.8 



103.7 



126.7 



147.7 



163.2 



From this it appears, that the more advanced age of the Male parent has a very 

 decided influence in occasioning a preponderance in the number of Male infants; 

 and, as the state of society generally involves a condition of this kind in regard 

 to marriages, whilst in the case of illegitimate children the same does not hold 

 good, the difference in the proportional number of male births is accounted for. 

 We are not likely to obtain data equally satisfactory in regard to the influence 

 of more advanced age on the part of the Female parent ; as a difference of 10 or 

 15 years on that side is not so common. If it exist to the same extent, it is 

 probable that the same law would be found to prevail in regard to Female 

 children born under such circumstances, as has been stated with respect to the 

 Male ; namely, that the mortality is greater during embryonic life and early 

 infancy, so that the preponderance is reduced. 



1018. There appears to be, from the first, a difference in the Viability (or 

 probability of life) of Male and Female children j for, out of the total number 

 born dead, there are 3 Males to 2 Females : this proportion gradually lessens, 

 however, during early infancy ; being about 4 to 3 during the first two months, 

 and about 4 to 5 during the next three months j after which time the deaths are 

 nearly in proportion to the numbers of the two sexes respectively, until the age 

 of puberty. The viability of the two sexes continues to increase during child- 

 hood j and attains its maximum between the 13th and 14th years. For a short 

 time after this epoch has been passed, the rate of mortality is higher in Females 

 than in Males j but from about the age of 18 to 28, the mortality is much greater 

 in Males, being at its maximum at 25, when the viability is only half what it 

 is at puberty. This fact is a very striking one ; and shows most forcibly that 

 the indulgence of the passions not only weakens the health, but in a great num- 

 ber of instances is the cause of a very premature death. From the age of 28 

 to that of 50, the mortality is greater and the viability less on the side of the 

 Female ; this is what would be anticipated from the increased risk to which she 

 is liable during the parturient period. After the age of 50, the mortality is 

 nearly the same for both. 



a. These facts have been expressed by Quetelet (Op. cit. ) in a form which brings them 

 prominently before the eye (Fig. 277). The relative viability of the male at different ages 

 is represented by a curved line ; the elevation of which indicates its degree at the respect- 

 ive periods marked along the base line. The dotted line, which follows a different curve, 

 represents the viability of the Female. Starting from a, the period of birth, we arrive at 

 the maximum of viability for both at b ; from this point, the Female curve steadily descends 

 towards n, at first very rapidly, but afterwards more gradually; whilst the Male curve does 

 not quite descend so soon, but afterwards falls much lower, its minimum being c, which 



'Annales d'Hygiene," Oct. 1829. 



2 "Law of Population," vol. ii. p. 343. 



