It is unnecessary here to magnify the functions of love in the world; it is sufficient to investigate its workings in its own proper sphere. It may, however, be worth while to quote a few expressions of thinkers, belonging to various schools, who have pointed out what seemed to them the far-ranging significance of the sexual emotions for the moral life. "The passions are the heavenly fire which gives life to the moral world," wrote Helvétius long since in _De l'Esprit_. "The activity of the mind depends on the activity of the passions, and it is at the period of the passions, from the age of twenty-five to thirty-five or forty that men are capable of the greatest efforts of virtue or of genius." "What touches sex," wrote Zola, "touches the centre of social life." Even our regard for the praise and blame of others has a sexual origin, Professor Thomas argues (_Psychological Review_, Jan., 1904, pp. 61-67), and it is love which is the source of susceptibility generally and of the altruistic side of life. "The appearance of sex," Professor Woods Hutchinson attempts to show ("Love as a Factor in Evolution," _Monist_, 1898), "the development of maleness and femaleness, was not only the birthplace of affection, the well-spring of all morality, but an enormous economic advantage to the race and an absolute necessity of progress. In it first we find any conscious longing for or active impulse toward a fellow creature." "Were man robbed of the instinct of procreation, and of all that spiritually springs therefrom," exclaimed Maudsley in his _Physiology of Mind_, "that moment would all poetry, and perhaps also his whole moral sense, be obliterated from his life." "One seems to oneself transfigured, stronger, richer, more complete; one _is_ more complete," says Nietzsche (_Der Wille zur Macht_, p. 389), "we find here art as an organic function: we find it inlaid in the most angelic instinct of 'love:' we find it as the 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."