Now will you reflect that the class of dreams which wake one up affords the best opportunity for establishing the influence of external disturbing stimuli. In most other cases it will be more difficult. We do not wake up out of all dreams, and if in the morning we remember a dream of the night before, how are we to assign it to a disturbing stimulus operating perhaps during the night? I once succeeded in subsequently establishing the occurrence of a sound-stimulus of this sort, but only, of course, because of peculiar circumstances. I woke up one morning at a place in the Tyrolese mountains knowing that I had dreamt that the Pope was dead. I could not explain the dream to myself, but later my wife asked me: “Did you hear quite early this morning the dreadful noise of bells breaking out in all the churches and chapels?” No, I had heard nothing, my sleep is too sound, but thanks to her telling me this I understood my dream. How often may such causes of stimulus as this induce dreams in the sleeper without his ever hearing of them afterwards? Possibly very often: and possibly not. If we can get no information of any stimulus we cannot be convinced on the point. And apart from this we have given up trying to arrive at an estimation of the sleep-disturbing external stimuli, since we know that they only explain a fragment of the dream and not the whole dream-reaction. We need not on that account give up this theory altogether; there is still another possible way of following it out. Obviously it is a matter of indifference what disturbs sleep and causes the mind to dream. If it cannot always be something external acting as a stimulus to one of the senses, it is possible that, instead, a stimulus operates from the internal organs—a so-called somatic stimulus. This supposition lies very close, and moreover it corresponds to the view popularly held with regard to the origin of dreams, for it is a common saying that they come from the stomach. Unfortunately, here again we must suppose that in very many cases information respecting a somatic stimulus operating during the night would no longer be forthcoming after waking, so that it would be incapable of proof. But we will not overlook the fact that many trustworthy experiences support the idea that dreams may be derived from somatic stimuli; on the whole it is indubitable that the condition of the internal organs can influence dreams. The relation of the content of many dreams to distention of the bladder or to a condition of excitation of the sex-organs is so plain that it cannot be mistaken. From these obvious cases we pass to others, in which, to judge by the content of the dream, we are at least justified in suspecting that some such somatic stimuli have been at work, since there is something in this content which can be regarded as elaboration, representation, or interpretation of these stimuli. Scherner, the investigator of dreams (1861), emphatically supported the view which traces the origin of