There is a headache of quite a different kind to which I must for a moment refer, that, namely, which depends entirely on imperfect vision, and for which spectacles are the remedy, not physic. The infirmity is not noticed during the first few years of life, but in later childhood, when a tolerably close attention to study has become necessary. Some of the minor degrees of short-sightedness, and want of power of adaptation of the eyes, such as exists in the aged, soon begin to interfere sensibly with the child's comfort, and the strain to which the eyes are subject produces a constant pain over the brow, the cause of which is often unsuspected.[13] In all cases, therefore, in which a child complains of constant pain over the brow for which there is no obvious cause, it is well to take the opinion of an oculist, who can best ascertain the power of _reading at different distances_ and with each eye separately, and the real cause of symptoms which had occasioned much anxiety is thus often brought to light. =Night Terrors.=--Before taking leave of the disorders of the nervous system, I must briefly mention the Nightmare, or Night Terrors of children, which often cause a degree of alarm quite out of proportion to their real importance. It happens sometimes that a child who has gone to bed apparently well, and who has slept soundly for a short time, awakes suddenly with a sharp and piercing cry. The child will be found sitting up in bed, crying out as if in an agony of fear, 'Oh dear! Oh dear! take it away! father! mother!' while terror is depicted on its countenance, and it does not recognise its parents, who, alarmed by the shrieks, have come into its room, but seems wholly occupied by the fearful impression that has roused it from sleep. By degrees consciousness returns; the child now clings to its mother or its nurse, sometimes wants to be taken up and carried about the room, and by degrees, sometimes in ten minutes, sometimes in half-an-hour, it grows quiet and falls asleep; and then usually the rest of the night is passed undisturbed, though sometimes a second or even a third attack may occur before daybreak. Seizures of this kind may come on in a great variety of circumstances, and may either happen only two or three times, or may continue to recur at intervals for several weeks. The great point, however, to bear in mind is that they depend invariably on some disorder of the stomach or bowels, and are never an evidence of the commencement of real disease of the brain. FOOTNOTES: [11] Reports of the Registrar-General, as quoted at p. 30 of my _Lectures on Diseases of Children_. The actual numbers are 9,350 under five years old, out of a total of 16,258. [12] Figures deduced from the 44th Report of the Registrar-General.