The Determination of Sex at Will.-- Although this has always been a question of great interest, and the subject of much experimentation, no rule can as yet be given by which the parents can know in advance of the birth of the child what the sex will be. Dr. Schenck's theory is that the ruling factor in determining the sex is the food partaken of by the mother. Furst believes that the differentiation may occur before, during, and a little while after the impregnation; that the chances of the development of one or another sex in one and the same woman may vary before final differentiation occurs. It is impossible to determine the sex of the embryo before the tenth week of fetal life. The cause of the differentiation, he believes, lies largely in the good or bad state of the health of the parents; in the first instance there being an excess of females, and in the latter an excess of males, relatively speaking. He believes that there is an excess of male children when conception takes place during the post-menstrual anemia. He has investigated one hundred and ninety-three cases carefully in regard to the probable date of conception after menstruation, and there is a notable increase of male births over female in the cases where conception occurred in the first five days after menstruation; that is to say, where the woman is not so well nourished as later. Dr. J. Griffith Davis gives as the result of her experiments in this direction, that when conception takes place three days before the menstrual period or within forty-eight hours afterward, the child will be a girl; when conception takes place ten days after the period, the child will be a boy. Although there are a greater number of the female than the male sex in all parts of the world where reliable statistics have been taken, in all civilized countries the proportion of male births is greater than that of females. There is a greater tendency of the male offspring to die earlier, and this is seen even before birth, in the proportion of three to two. For this reason the stronger sex as applied to men has been regarded by some authors as a misnomer. They are physically weaker in early life and succumb more readily to noxious influences. The relative age of the parents is said to be another factor in determining the sex of the children. Seniority on the father's side gives an excess of male children; equality in the age of the parents gives a slight preponderance of females; seniority on the mother's side gives an excess of females. Men, and especially scholars, who pass a sedentary life and who exhaust their nervous force to a great extent, beget more girls than boys; so, also, a very advanced age on the part of the man diminishes the number of male offspring.