Man, more than any other animal, depends upon his sense of sight, for in his case the other senses, such as smell and hearing, are more or less "atrophied," or stunted, as compared with their keenness in other animals. They are sometimes almost lost through lack of use. To a certain extent this is true of the sense of sight also, but it is less true here than in the other instances, the conditions of modern life requiring the almost constant use of the organs of vision.