Though love, even in its average manifestations, is inseparable from obsession and impulsion, I see in these two characteristics no legitimate reason for placing it unrestrictedly—as some writers have been pleased to do—in the category of pathology.[161] It has its natural end, and tends to fulfil it by appropriate means. Every one knows that it sometimes reaches the confines of madness; but in this it does not differ from the majority of the emotions. There are the impulsive and irresistible forms of love (erotomania), but they remain within natural limits; the true pathology of love is elsewhere—outside nature. Footnote 161: See Danville, _Psychologie de l’amour_, ch. vi., for a detailed discussion of this question, which the author also answers in the negative. On the deviations and interversions of the sexual instinct so many observations have been published,—especially in our own day,—so many books written, so many medico-legal theses discussed, that we might think the psychology of the subject had thereby been cleared up. Nothing of the sort; and it is this alone which interests us. Reduced to its simplest expression, the psychological problem is this: The sex-instinct having a clearly-defined and easily-verifiable end, how can it deviate therefrom? Other instincts—that of conservation under its offensive and defensive forms, that of self-feeling—have no mechanism exclusively appropriated to them, and are susceptible of various and multiple adaptations. This, on the contrary, is confined by nature within strict limits. No doubt every instinct has its oscillations; but it is only the means which vary, the end remains the same. The ant, the bee, the beaver, the spider, modify their manner of acting in accordance with their environment, because they are confronted with the dilemma that they must either adapt themselves or perish; but they always arrive at the same end. The nutritive instinct in man utilises animals and vegetables—the raw caterpillars of the savage or the scientific cookery of the civilised man—but the same end is always aimed at and attained. With the deviations—at least the extreme ones—of the sex-instinct it is otherwise: everything changes, means and end alike. The normal end, generation and the perpetuity of the species, is ignored or annihilated. This aspect of the question does not appear to me to have been sufficiently noticed. How can an instinct so solidly based, and having its own special mechanism, go astray?