Having thus pointed out that there are more women actually living in the world than men, although a larger number of boys are born than girls, we will consider for a moment some of the laws of nature which determine the number of the sexes. Without giving the figures,--which would make dry reading,--we will state in brief the conclusions derived from many observations, extending over many years and many nationalities. The relative age of the parents has an especial influence upon the sex of the children. Seniority on the father's side gives excess of male offspring. Equality in the parents' age gives a slight preponderance of female offspring. Seniority on the mother's side gives excess of female offspring. This tallies with the fact that in all civilized countries, as has been stated, the proportion of male births is greater than that of females; for, in accordance with the customs of society, the husband is generally older than the wife. A curious instance, in confirmation of this law, has recently come under our observation. A patient, married for the second time, is ten years older than her husband. She has two children by him, both girls. Singular to relate, her former husband was ten years older than herself, and by him she had four children, of whom three were boys, the fourth (a girl) having a twin brother. Still, the relative age is not the sole cause which fixes the sex of the child. Its operation is sometimes overruled by conflicting agencies. In some districts of Norway, for example, there has been a constant deficiency in boys, while in others the reverse has been the case. The circumstance is well known, that after great wars, and sometimes epidemics, in which a disproportionate number of men have died, more boys are born than usual. Men who pass a sedentary life, and especially scholars who exhaust their nervous force to a great extent, beget more girls than boys. So, also, a very advanced age on the man's side diminishes the number of males among the offspring. The quantity and the quality of the food; the elevation of the abode; the conditions of temperature; the parents' mode of life, rank, religious belief, frequency of sexual intercourse,--have all been shown to be causes contributing to the disproportion of the sexes, besides the relative ages of the parents. Some writers have stated that a southerly or warm and humid constitution of the year is most favorable to the birth of female infants, while in cold and dry years most males are produced. This statement has not been supported by trustworthy statistics in regard to the human race, but in respect of domestic animals the agriculturists of France have long observed that the season has much to do with the sex. When the weather is dry and cold, and the wind northerly, mares, ewes, and heifers produce more males than when the opposite meteorological condition prevails.