Headache.--Headache may be due to so many different causes that it would be impossible in this little book to adequately consider them, but it would not be fair to omit to mention that in many cases the headache of young people is due to their want of spectacles. The idea that spectacles are only required by people advanced in life is by this time much shaken, but even now not only many parents object to their children enjoying this most necessary assistance to imperfect vision, but also employers may be found so foolish and selfish as to refuse to employ those persons who need to wear glasses. The folly as well as selfishness of this objection is demonstrated by the far better work done by a person whose vision has been corrected, and the absolute danger incurred by all who have to deal with machinery if vision is imperfect. Among other causes for headache are the defects of mouth, throat, stomach, and bowels already described, because in all of them there is a supply of septic material to the blood which naturally causes headache and other serious symptoms. Abnormalities of Menstruation.--The normal period should occur at regular intervals about once a month. Its duration and amount vary within wide limits, but in each girl it should remain true to her individual type, and it ought not to be accompanied by pain or distress. As a rule the period starts quite normally, and it is not until the girl's health has been spoiled by over-exertion of body or mind, by unwise exertion during the period, or by continued exposure to damp or cold, that it becomes painful and abnormal in time or in amount. One of the earliest signs of approaching illness--such as consumption, anæmia, and mental disorder--is to be found in the more or less sudden cessation of the period. This should always be taken as a danger-signal, and as indicating the need of special medical advice. Another point that should enter into intimate talk with girls is to make them understand the co-relation of their own functions to the great destiny that is in store. A girl is apt to be both shocked and humiliated when she first hears of menstruation and its phenomena. Should this function commence before she is told about it, she will necessarily look upon it with disgust and perhaps with fear. It is indeed a most alarming incident in the case of a girl who knows nothing about it, but if, before the advent of menstruation, it be explained to her that it is a sign of changes within her body that will gradually, after the lapse of some years, fit her also to take her place amongst the mothers of the land, her shame and fear will be converted into modest gladness, and she will readily understand why she is under certain restrictions, and has at times to give up work or pleasure in order that her development may be without pain, healthy, and complete. CHAPTER IV. MENTAL AND MORAL TRAINING.