We have already shown in rude outline how a difference (apparently chemical) between two fertilized eggs starts them along two different lines of development in the embryonic stage. One develops the characteristic male primary and secondary sex characters, the other the female. Throughout the embryonic or intra-maternal stage this differentiation goes on, becoming more and more fixed as it expresses itself in physical structures. Childhood is only a continuation of this development—physically separate from the mother after the period of lactation. Until puberty, when sex ceases to be merely potential and becomes functional (about 12-14 in girls and 14-16 boys), the differences in metabolism are not very marked. Neither are they in old age, after sex has ceased to be functional. It is during the period when sex is functional (about 35 years in women and considerably longer in men) that the gross physiological differences manifest themselves.
Before puberty in both sexes, calcium or lime salts are retained in the tissues and go to build up the bony skeleton. (A mere sketch of calcium metabolism is all that can be given here—for details consult such works as and [17] in bibliography; summary in [14; pp. 34f. & 161f.]) Note that puberty comes earlier in girls than in boys, and that the skeleton therefore remains lighter. During the reproductive period in women these salts are heavily drawn upon for the use of the reproductive system. The male reproductive system draws upon them as well, though the drain is very slight as compared to that in women. In old age these salts produce senility through deposit in the tissues, especially in the arteries.
At the pubertal age in girls begins the phenomenon known as menstruation, in which there is a large excretion of calcium salts. In pregnancy these are needed for building the skeleton of the foetus, and at delivery go to the breasts to assist in lactation. Bell states that there is a noticeable connection between early menstruation and short stature, and vice versa. What is commonly known as menstruation lasts only a few days, and is merely the critical period in a monthly cycle or periodicity which goes with the female sex specialization. This period involves the gradual preparation of the uterus or womb for a guest, together with the maturing of the ova. Then the Graafian follicles containing the ova break and these latter enter the uterus for fertilization.
If fertilization takes place, the fertilized egg buries itself in the wall and development of the embryo proceeds. Menstruation stops, the calcium salts being required for the growing embryo. There is likely to be no menstruation for a considerable time after delivery if the child is nursed, as is normal. This gives the uterus time for devolution to the normal, before a surplus of calcium salts sets the periodicity going again. If the egg which passes from the ovary to the uterus is not fertilized, it is excreted, the uterus goes through another monthly cycle of preparation for the period of intra-maternal environment, and so on indefinitely until the climacteric.
This climacteric or decay of sexuality is a rather critical time, especially in women. It marks the period at which the metabolism can no longer support the strain of reproduction. A surplus of calcium brings on senility, as noted above. Withdrawal of the interests which centre in sex, together with the marked accompanying physical changes, involves a shift of mental attitude which is also frequently serious. A British coroner stated in the British Medical Journal in 1900 (Vol. 2, p.792) that a majority of 200 cases of female suicide occurred at this period, while in the case of younger women suicide is peculiarly likely to occur during menstruation. Krugelstein and Lombroso, respectively, remark the same tendencies.[[18]].
It is a matter of almost everyday observation that men and women in the neighbourhood of fifty suddenly find themselves disoriented in the world. Tolstoi, for example, who had written passionately of passion in his earlier years, suddenly awoke, according to his "Confessions," from what seemed to him afterward to have been a bad dream. In this case, the result was a new version of religion as a new anchorage for the man's life. It may be pacifism, prohibition, philanthropy, or any one of a very large number of different interests—but there must usually be something to furnish zest to a life which has ceased to be a sufficient excuse for itself.
If freed from worry about economic realities, it is not infrequently possible for the first time for these people to "balance" their lives—to find in abstraction a rounded perfection for which earlier in life we seek in vain as strugglers in a world of change. Thus old people are often highly conservative, i.e., impatient of change in their social environment, involving re-orientation; they wish the rules of the game let alone, so they can pursue the new realities they have created for themselves.
Socially, the old are of course a very important factor since a changed metabolism sets them somewhat outside the passionate interests which drive people forward, often in wrong directions, in the prime of life. Hence in a sense the old can judge calmly, as outsiders. Like youth before it has yet come in contact with complicated reality, they often see men and women as "each chasing his separate phantom."
While such conservatism, in so far as it is judicial, is of value to society, looking at it from the viewpoint of biology we see also some bad features. Senex, the old man, often says to younger people, "These things you pursue are valueless—I too have sought them, later abandoned the search and now see my folly;" not realizing that if his blood were to resume its former chemical character he would return to the quest.
Elderly people, then, biological neuters, come especially within the problem of the economical use of the social as distinguished from the biological capacities of the race. They affect the sex problem proper, which applies to a younger age-class, only through their opinions. Some of these opinions are hangovers from the time in their own lives when they had stronger sexual interests, and some are peculiar to people of their readjusted glandular activity. Their reproductive contribution to society has been made.