This digression brings us into a field of inquiry—that of the psychical conditions of social life—which during recent years has been the object of certain most important scientific researches. The investigations into the psychology of masses, as well as the experiments on suggestive therapeutics, have proved to how great an extent mental states may be transmitted from individual to individual by unconscious imitation of the accompanying movements. The doctrine of universal sympathy, a clear statement of which was given long ago in the ethical theory of Adam Smith,[97] has thus acquired a psychological justification in the modern theories of imitative movement. Contemporary science has at last learned to appreciate the fundamental importance of imitation for the development of human culture.[98] And some authors have even gone so far as to endeavour to deduce all sociological laws from this one principle. At the same time natural history has begun to pay more and more attention to the indispensability of imitation for the full development of instincts, as well as for training in those activities which are the most necessary in life.[99] It is fortunate for the theory of art that the importance of the imitative functions has thus been simultaneously acknowledged in various departments of science. Whatever one may think of the somewhat audacious generalisations which have been made in the recent application of this new principle, it is incontestable that the æsthetic activities can be understood and explained only by reference to universal tendency to imitate. It is also significant that writers on æsthetic had felt themselves compelled to set up a theory of imitation long before experimental psychologists had begun to turn their attention in this direction. In Germany the enjoyment of form and form-relations has since Vischer’s time been interpreted as the result of the movements by which not only our eye, but also our whole body, follows the outlines of external things.[100] In France Jouffroy stated the condition for the receiving of æsthetic impressions to be a “power of internally imitating the states which are externally manifested in living nature.”[101] In England, finally, Vernon Lee and Anstruther Thompson have founded a theory of beauty and ugliness upon this same psychical impulse to copy in our own unconscious movements the forms of objects.[102] And in the writings of, for instance, Home,[103] Hogarth,[104] Dugald Stewart,[105] and Spencer,[106] there can be found a multitude of isolated remarks on the influence which is in a direct way exercised on our mental life by the perception of lines and forms.