I pass on to a less frequent phenomenon, which shows us at once intense imagination during sleep, and a lasting imprint left by these imaginations upon the waking organism;--an unintended self-suggestion which we may compare with Stevenson's voluntary self-suggestion mentioned just above. The permanent result of a dream, I say, is sometimes such as to show that the dream has not been a mere superficial confusion of past waking experiences, but has had an unexplained potency of its own,--drawn, like the potency of hypnotic suggestion, from some depth in our being which the waking self cannot reach. Two main classes of this kind are conspicuous enough to be easily recognised--those, namely, where the dream has led to a "conversion" or marked religious change, and those where it has been the starting-point of an "insistent idea" or of a fit of actual insanity.[40] The dreams which convert, reform, change character and creed, have of course a _primâ facie_ claim to be considered as something other than ordinary dreams; and their discussion may be deferred till a later stage of our inquiry. Those, on the other hand, which suddenly generate an insistent idea of an irrational type are closely and obviously analogous to post-hypnotic self-suggestions, which the self that inspired them cannot be induced to countermand. Such is the dream related by M. Taine,[41] where a gendarme, impressed by an execution at which he has assisted, dreams that he himself is to be guillotined, and is afterwards so influenced by the dream that he attempts suicide. Several cases of this kind have been collected by Dr. Faure;[42] and Dr. Tissié, in his interesting little work, _Les Rêves_, has added some curious instances from his own observation. A striking illustration may be drawn from the following incident in the story of Krafft-Ebing's patient,[43] Ilma S., the genuineness of whose stigmata seems proved by that physician's care in observation, and by the painfulness of certain experiments performed upon her by students as practical jokes and against her will:--