All knowledge of things, of their properties, their names, their uses, their meanings, consists in supplementing our consciousness of those qualities which they present to our senses, by images previously obtained through any senses. The force of this supplementing can be understood from the drawings of children and primitive peoples. That which appears in the field of vision is often left unrepresented. Linear perspective, for instance, does not exist in such drawings, although it is a part of the sensory impression. On the other hand, many things are given by the draughtsman which are invisible under the circumstances of the situation, but which he regards as essential parts of the thing because of their practical importance: for instance, both eyes of a person seen in profile, equal length of all the legs of tables and chairs, equal size of things at a distance and things near by. The significance of this supplementing by ideas is illustrated also in pathological cases. It happens that some of the associative connections in the brain are destroyed by disease, reducing the mind to a condition like that of early childhood, when direct sense impressions alone determined action. Patients may see the shape and color of a thing correctly, may even be able to draw it or paint it, but are unable to tell the name of the object, although they are perfectly familiar with it. They cannot answer our question as to what purpose the thing serves; possibly they give ridiculous answers, fitting an altogether different thing. Only when they are permitted to use the kinesthetic and tactual senses by taking the thing in their hands, do they recognize it. In other cases the patient, although possessing his normal sensibility to touch, is unable to recognize things by his hands alone, but recognizes them at once when permitted to open his eyes.