To the early Protestant mind, as illustrated by Luther, there was something diseased, though not impure, in sexual excitement during sleep; thus, in his _Table Talk_ Luther remarks that girls who have such dreams should be married at once, "taking the medicine which God has given." It is only of comparatively recent years that medical science has obtained currency for the belief that this auto-erotic process is entirely normal. Blumenbach stated that nocturnal emissions are normal.[234] Sir James Paget declared that he had never known celibate men who had not such emissions from once or twice a week to twice every three months, both extremes being within the limits of good health, while Sir Lauder Brunton considers once a fortnight or once a month about the usual frequency, at these periods the emissions often following two nights in succession. Rohleder believes that they may normally follow for several nights in succession. Hammond considers that they occur about once a fortnight.[235] Ribbing regards ten to fourteen days as the normal interval.[236] Löwenfeld puts the normal frequency at about once a week;[237] this seems to be nearer the truth as regards most fairly healthy young men. In proof of this it is only necessary to refer to the exact records of healthy young adults summarized in the study of periodicity in the present volume. It occasionally happens, however, that nocturnal emissions are entirely absent. I am acquainted with some cases. In other fairly healthy young men they seldom occur except at times of intellectual activity or of anxiety and worry. Lately there has been some tendency for medical opinion to revert to the view of Luther, and to regard sexual excitement during sleep as a somewhat unhealthy phenomenon. Moll is a distinguished advocate of this view. Sexual excitement during sleep is the normal result of celibacy, but it is another thing to say that it is, on that account, satisfactory. We might, then, Moll remarks, maintain that nocturnal incontinence of urine is satisfactory, since the bladder is thus emptied. Yet, we take every precaution against this by insisting that the bladder shall be emptied before going to sleep. (_Libido Sexualis_, Bd. I, p. 552.) This remark is supported by the fact, to which I find that both men and women can bear witness, that sexual excitement during sleep is more fatiguing than in the waking state, though this is not an invariable rule, and it is sometimes found to be refreshing. In a similar way, Eulenburg (_Sexuale Neuropathie_, p. 55) states that nocturnal emissions are no more normal than coughing or vomiting.