Although, for certain purposes, it is necessary to consider the ganglionic and cerebro-spinal system together, as parts of a single apparatus, it is important also to remember the boundaries that lie between them. It is much easier, by intense muscular exertion, that necessitates evolution of force in the spinal cord, to render the brain incapable of function, than to do so by intense action of the ganglionic nerves, whose connection with the brain, though real, is much less direct. Were it not so, life would be much more precarious than it is, and advance in civilization impossible; because the necessarily incessant activity of the nerves involved in nutritive processes would too largely impair the action of the brain. The effect on the brain of a really irresistible and predominant activity of the nerves involved in the reproductive organs, is to be studied in the lower animals, and in phenomena that, fortunately, are rarely to be observed in healthy individuals of the human race. Still less can such confessedly morbid predominance be considered as a peculiar liability of the female sex in this race. A singular tendency exists in many quarters, and is strongly manifested in Dr. Clarke's book, to assume that considerations pertaining to sex and to the functions of reproduction exercise such an enormous influence upon one sex, and none at all upon the other. Since the discovery in 1827 of the ovule or female reproductive cell, there can be no question of the complete physiological equivalence and analogy between the essential organs of reproduction in the two sexes. The period of their development, the influence of such development on the entire nutrition of the body, the irregularities of nutritive or of cerebro-spinal action, that may be caused by irregularities in such development, are also completely analogous. It is only the organ of gestation that is peculiar to the female--the organ of maternity--the function that, although resulting from sex, transcends sex and belongs to the race. In a double sense is the uterus secondary to the ovaries.[41] For its physiological action, both in menstruation and in pregnancy, is the direct consequence of ovarian functions, and closely dependent upon them; and the period of its prominent activity does not come until after the action of the ovaries has been completely established; that is, the period of maternity is, or should be, consecutive to the period of adolescence, and the work of gestation only entered upon when the work of ovulation has long been thoroughly accomplished.