forward into this region when very exceptional in character, as when respiration or digestion is impeded, or when we make a special effort of attention to single them out.[85] When we are asleep, however, and the avenues of external perception are closed, they assume greater prominence and distinctness.  The centres, no longer called upon to react on stimuli coming from without the organism, are free to react on stimuli coming from its hidden recesses.  So important a part, indeed, do these organic feelings take in the dream-drama, that some writers are disposed to regard them as the great, if not the exclusive, cause of dreams.  Thus, Schopenhauer held that the excitants of dreams are impressions received from the internal regions of the organism through the sympathetic nervous system.[86]

It is hardly necessary, perhaps, to give many illustrations of the effect of such organic sensations on our dreams.  Among the most common provocatives of dreams are sensations connected with a difficulty in breathing, due to the closeness of the air or to the pressure of the bed-clothes on the mouth.  J. Boerner investigated the influence of these circumstances by covering with the bed-clothes the mouth and a part of the nostrils of persons who were sound asleep.  This was followed by a protraction of the act of breathing, a reddening of the face, efforts to throw off the clothes, etc.  On being roused, the sleeper testified that he had experienced a nightmare, in which a horrid animal seemed to be weighing him down.[87] Irregularity of the heart’s action is also a frequent cause of dreams.  It is not improbable that the familiar dream-experience of flying arises from disturbances of the respiratory and circulatory movements.

Again, the effects of indigestion, and more particularly stomachic derangement, on dreams are too well known to require illustration.  It may be enough to allude to the famous dream which Hood traces to an excessive indulgence at supper.  It is known that the varying condition of the organs of secretion influences our dream-fancy in a number of ways.

Finally, it is to be observed that an injury done to any part of the organism is apt to give rise to appropriate dream-images.  In this way, very slight disturbances which would hardly affect waking consciousness may make themselves felt during sleep.  Thus, for example, an incipient toothache has been known to suggest that the teeth are being extracted.[88]

It is worth observing that the interpretation of these various orders of sensations by the imagination of the dreamer takes very different forms according to the person’s character, previous experience, ruling emotions, and so on.  This is what is meant by saying that during sleep every man has a world of his own, whereas, when awake, he shares in the common world of perception.

Dream-Exaggeration.