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]
Loewenfeld 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.

Nocturnal emissions are usually, though not invariably, accompanied by
dreams of a voluptuous character in which the dreamer becomes conscious in
a more or less fantastic manner of the more or less intimate presence or
contact of a person of the opposite sex. It would seem, as a general rule,
that the more vivid and voluptuous the dream, the greater is the physical
excitement and the greater also the relief experienced on awakening.
Sometimes the erotic dream occurs without any emission, and not
infrequently the e