We have seen that the distinction between "sadism" and "masochism" cannot be maintained; not only was even De Sade himself something of a masochist and Sacher-Masoch something of a sadist, but between these two extreme groups of phenomena there is a central group in which the algolagnia is neither active nor passive. "Sadism" and "masochism" are simply convenient clinical terms for classes of manifestations which quite commonly occur in the same person. We have further found that--as might have been anticipated in view of the foregoing result--it is scarcely correct to use the word "cruelty" in connection with the phenomena we have been considering. The persons who experience these impulses usually show no love of cruelty outside the sphere of sexual emotion; they may even be very intolerant of cruelty. Even when their sexual impulses come into play they may still desire to secure the pleasure of the persons who arouse their sexual emotions, even though it may not be often true that those who desire to inflict pain at these moments identify themselves with the feelings of those on whom they inflict it. We have thus seen that when we take a comprehensive survey of all these phenomena a somewhat general formula will alone cover them. Our conclusion so far must be that under certain abnormal circumstances pain, more especially the mental representation of pain, acts as a powerful sexual stimulant. The reader, however, who has followed the discussion to this point will be prepared to take the next and final step in our discussion and to reach a more definite conclusion. The question naturally arises: By what process does pain or its mental representation thus act as a sexual stimulant? The answer has over and over again been suggested by the facts brought forward in this study. Pain acts as a sexual stimulant because it is the most powerful of all methods for arousing emotion.