greatest stimulant of life.... It is not merely that it changes the feeling of values: the lover _is_ worth more, is stronger. In animals this condition produces new weapons, pigments, colors, and forms, above all new movements, new rhythms, a new seductive music. It is not otherwise in man.... Even in art the door is opened to him. If we subtract from lyrical work in words and sounds the suggestions of that intestinal fever, what is left over in poetry and music? _L'Art pour l'art_ perhaps, the quacking virtuosity of cold frogs who perish in their marsh. All the rest is created by love." It would be easy to multiply citations tending to show how many diverse thinkers have come to the conclusion that sexual love (including therewith parental and especially maternal love) is the source of the chief manifestations of life. How far they are justified in that conclusion, it is not our business now to inquire. It is undoubtedly true that, as we have seen when discussing the erratic and imperfect distribution of the conception of love, and even of words for love, over the world, by no means all people are equally apt for experiencing, even at any time in their lives, the emotions of sexual exaltation. The difference between the knight and the churl still subsists, and both may sometimes be found in all social strata. Even the refinements of sexual enjoyment, it is unnecessary to insist, quite commonly remain on a merely physical basis, and have little effect on the intellectual and emotional nature.[68] But this is not the case with the people who have most powerfully influenced the course of the world's thought and feeling. The personal reality of love, its importance for the individual life, are facts that have been testified to by some of the greatest thinkers, after lives devoted to the attainment of intellectual labor. The experience of Renan, who toward the end of his life set down in his remarkable drama _L'Abbesse de Jouarre_, his conviction that, even from the point of view of chastity, love is, after all, the supreme thing in the world, is far from standing alone. "Love has always appeared as an inferior mode of human music, ambition as the superior mode," wrote Tarde, the distinguished sociologist, at the end of his life. "But will it always be thus? Are there not reasons for thinking that the future perhaps reserves for us the ineffable surprise of an inversion of that secular order?" Laplace, half an hour before his death, took up a volume of his own _Mécanique Celeste_, and said: "All that is only trifles, there is nothing true but love." Comte, who had spent his life in building up a Positive Philosophy which should be absolutely real, found (as indeed it may be said the great English Positivist Mill also found) the culmination of all his ideals in a woman, who was, he said, Egeria and Beatrice and Laura in one, and he wrote: "There is nothing real in the world but love.