It is especially the extensive developmental processes in the ovary, influencing the nerves of that organ, which give rise to centripetal stimuli and evoke reflex manifestations. In the working of the circulatory system, such influences are apparent; and during the menarche, some time already before the first onset of menstruation, variations occur in the blood-pressure, and these during menstruation take the form of a typical undulatory curve. [Illustration: FIG. 47.—Horizontal section through the female breast. (From Toldt: Atlas of Human Anatomy.—Rebman Company, New York.) ] Thus it becomes comprehensible that even in healthy girls, the first appearance of the catamenia and likewise the expectation of the flow induce a certain modification and alteration in the whole nature and disposition. Girls often lose their previous cheerful and lively character, becoming quiet, self-absorbed, sometimes even melancholy; they are disinclined for study, have a repugnance to all sustained physical or mental activity, become annoyed and snappish on slight occasion, are restless at night, consider themselves to be ailing, and so on. During the first menstruation girls commonly appear pale and anxious, they have blue lines beneath the eyes, the face has a tired aspect, the movements lack energy, and a general want of tone combined with an abnormal irritability may be noticed. Some days before the first menstruation, the vulva, the labia majora and minora, and the vaginal mucous membrane, are swollen, the clitoris becomes conspicuous in consequence of erectile processes, a slight secretion appears in the genital passage, and the breasts become sensitive and slightly turgid. The urine deposits a thick sediment, and occasionally severe strangury is observed. In many cases, also, digestive disturbances occur, loss of appetite, constipation, or a tendency to diarrhœa. The first menstruation usually lasts four or five days. On the first day the discharge is blood-stained mucus, thereafter becoming sanguineous. In some cases, the bleeding at the first menstruation is profuse and of long duration. It is not always after the first menstruation that the subsequent discharges follow at the regular intervals of four weeks. In delicate, anæmic girls the second menstruation may not occur till several months have elapsed after the first; less often the second menstruation ensues a fortnight after the first, or even earlier.