For the present we will leave the ‘meaning’ of the dream out of question, and try instead, by starting from the common element in dreams, to clear a path to a better understanding of their nature. From the relationship of dreams to sleep we have drawn the conclusion that dreams are the reaction to a stimulus disturbing sleep. As we have heard, this is also the single point at which exact experimental psychology can come to our aid; it affords proof of the fact that stimuli brought to bear during sleep make their appearance in dreams. Many investigations have been made on these lines, culminating in those of Mourly Vold whom I mentioned earlier; we have all, too, been in a position to confirm their results by occasional observations of our own. I will choose some of the earlier experiments to tell you. Maury had tests of this kind carried out upon himself. Whilst dreaming, he was made to smell some eau de Cologne, whereupon he dreamt he was in Cairo, in the shop of Johann Maria Farina, and this was followed by further crazy adventures. Again, someone gave his neck a gentle pinch, and he dreamt of the application of a blister and of a doctor who had treated him when he was a child. Again, they let a drop of water fall on his forehead and he was immediately in Italy, perspiring freely and drinking the white wine of Orvieto. The striking feature about these dreams produced under experimental conditions will perhaps become still clearer to us in another series of “stimulus”-dreams. These are three dreams of which we have an account by a clever observer, Hildebrandt, and all three are reactions to the sound of an alarum-clock: “I am going for a walk on a spring morning, and I saunter through fields just beginning to grow green, till I come to a neighbouring village, where I see the inhabitants in holiday attire making their way in large numbers to the church, their hymn-books in their hands. Of course! it is Sunday and the morning service is just about to begin. I decide to take part in it, but first as I am rather overheated I think I will cool down in the churchyard which surrounds the church. Whilst reading some of the epitaphs there I hear the bell-ringer go up into the tower, where I now notice, high up, the little village bell which will give the signal for the beginning of the service. For some time yet it remains motionless, then it begins to swing, and suddenly the strokes ring out, clear and piercing—so clear and piercing that they put an end to my sleep. But the sound of the bell comes from the alarum-clock.”