=Power of Sense Perception Limited: A. By Interest.=--It should be noted, however, that so far as our actual life needs are concerned, there is no large demand for an all-round ability to interpret sensuous impressions. For practical purposes, men are interested in different objects in quite different ways. One is interested in the colour of a certain wood, another in its smoothness, a third in its ability to withstand strain, while a fourth may even be interested in more hidden relations, not visible to the ordinary sense. This will justify one in ignoring entirely qualities in the object which are of the utmost importance to others. From such a practical standpoint, it is evidently a decided gain that a person is not compelled to see everything in an object which its sensuous attributes might permit one to discover in it. In the case of the man with the so-called untrained sense, therefore, it is questionable whether the failure to see, hear, etc., is in many cases so much a lack of ability to use the particular sense, as it is a lack of practical interest in this phase of the objective world. In such processes as induction and deduction, also, it is often the external relations of objects rather than their sensory qualities that chiefly interest us. Indeed, it is sometimes claimed that an excessive amount of mere training in sense discrimination might interfere with a proper development of the higher mental processes. =B. By Knowledge.=--From what has been discovered regarding the learning process, it is evident that the development of any sense, as sight, sound, touch, etc., is not brought about merely by exercising the particular organ. It has been learned, for instance, that the person who is able to observe readily the plant and animal life as he walks through the forest, possesses this skill, not because his physical eye, but because his mind, has been prepared to see these objects. In other words, it is because his knowledge is active along such lines that his eye beholds these particular things. The chief reason, therefore, why the exercise of any sense organ develops a power to perceive through that sense, is that the exercise tends to develop in the individual the knowledge and interest which will cause the mind to react easily and effectively on that particular class of impressions. A sense may be considered trained, therefore, to the extent to which the mind acquires knowledge of, and interest in, the objective elements. CHAPTER XXVI MEMORY AND APPERCEPTION