The third fact mentioned is also illustrated by this type; the fact that mental instruction and derangement may come easily, through the stress laid upon vision in the person's mental economy. I need not enlarge upon the different forms of special defect which come through impairment of sight by central lesion or degeneration of the visual centers and connections. Suffice it to say that they are very common, and very difficult of recovery. The visual person is often so completely a slave to his sight that when that fails either in itself or through weakness of attention he becomes a wreck off the shore of the ocean of intellect. When we consider the large proportion just mentioned of pupils of this type, the care which should be exercised by the school authorities in the matter of favourable conditions of light, avoidance of visual fatigue, proper distance-adjustments in all visual application as regards focus, symmetry, size of objects, copies, prints, etc., becomes at once sufficiently evident to the thoughtful teacher, as it should be still earlier to the parent. There should be a medical examination, by a competent oculist, before the child goes to school, and regular tests afterward. School examiners and boards should have qualifications for reporting on the hygienic conditions of the school as regards lighting. The bright glare of a neighbouring wall before a window toward which children with weak eyes face when at their desks may result not only in common defects of vision but also in resulting mental and moral damage; and the results are worse to those who depend mainly on vision for the food, drink, and exercise, so to speak, of their growing minds. As to the methods of teaching these and also the other sensory pupils, the indications already given must suffice. The statement of some of these far-reaching problems of educational psychology, and of the directions in which their answers are to be sought, exhausts the purpose of this chapter. In general it may be said that the recommendations made for the treatment of sensory children at the earlier stage may be extended to later periods also, and that the treatment should be, for the most part, in intelligent contrast to that which the motor pupils receive.