The formation of new follicles continues only for a short time after birth, when the Graafian follicles are the most numerous; the entire number contained within the ovaries of the child being estimated at over 70,000. In view of the unquestionably large number of follicles in very young ovaries, and the relatively small number of ova which reach maturity, the degeneration of many follicles after reaching a certain degree of development seems certain. CHAPTER IV. PHYSIOLOGY OF THE FEMALE GENERATIVE ORGANS. Ovulation; Etiology of Menstruation; Uterine Nerve-supply; the Function of the Uterus; Stages of the Menstrual Cycle; Average Duration of the Menstrual Flow; Character of tahe Flow; Relation of Ovulation to Menstruation; the Menstrual Wave; Definition of Menstruation; Premomitory Symptoms of the Flow; Hygiene of Menstruution. "Toil and grow strong; by toil the flaccid nerves Grow firm, and gain a more compacted tone." -- ARMSTRONG. Ovulation.-- At birth the formation of the ova is nearly completed; the production of' new cells probably ceases after the second year. The ovaries of the child of two years contain, therefore, the full quota of ova, although the vast majority of these cells always remain immature and undeveloped. While it is probable that a variable number of the immature ova undergo partial development before puberty, yet the advent of sexual maturity at that time marks the establishment of the regular development of the Graafian follicles and their contained ova, accompanied by the attendant phenomena of menstruation. During the entire child-bearing period, or from about the age of fifteen to forty-five years, the development of the Graafian follicles and the discharge of the ova are continually taking place. The liberation of the ova usually takes place at definite times, which in general coincide with the menstrual epochs, one or more ova being set free at each period; but this is by no means invariable. The ripe human ovum or germ cell is a spheric cell, about 0.2 mm. in diameter, consisting of granular protoplasm, in which lies a nucleus which contains the germinal spot. The proper cell-wall is a structure of great delicacy, outside of which is a secondary envelope. Menstruation.-- The etiology of menstruation has been variously explained at different epochs. The chief theories have been that of plethora, and the ovulation, the tubal, and the nerve theories. First, the Theory of Plethora.-- From the time of Hippocrates to 1835 the theory prevailed that in the female body the formation of blood is sufficiently rich to provide every four weeks for an overflow of the same, the evacuation of which becomes a necessity. It was believed that this excess of blood depended on an excess of formative power in the woman.