I have no intention of describing the ordinary, familiar phenomena of fear. These, in both their psychological and physiological manifestations, will be found adequately treated in any good text-book on the emotions. What I wish to do, rather, is to call attention to some little-known facts which find scant mention in the text-books for the excellent reason that it is only within the past few years that they have been made part of organised knowledge. Yet they are facts of the utmost significance from both a theoretical and a practical point of view; and, indeed, an understanding of them is of no less importance to the layman than to the scientist. Their discovery has made possible for the first time what may be called an applied psychology of fear—that is to say, a statement of principles the application of which will go far toward solving the problem of how to avert the evil consequences of fear without the loss of its really beneficial qualities. That there is a certain virtue in fear requires no scientific demonstration. Fear, as everybody ought to be aware, is intrinsically one of the most useful of emotions. It is an instinct implanted in us as a prime aid in the struggle for existence. Doubtless for this reason it is, as compared with the other emotions, the earliest to make its appearance in the newborn child. Preyer, whose book, “The Mind of the Child,” is not nearly so well known in this country as it should be, puts the first manifestation of fear in an infant at the twenty-third day after birth. Other observers, including Charles Darwin, have found no indications of it until somewhat later than this. But all agree that it is the first emotion, properly so called, to show itself, and that its normal function is to instil caution and prudence in relation to objects and actions that might have destructive effects.