Dreams aroused by odours do not usually seem to occur except on the experimental application of them to the sleeper's nostrils, and experiments in this direction are not usually successful.[65] Occasionally, however, smell dreams occur without any traceable sensory source, and Grace Andrews, for instance, records a dream of the sea, accompanied by the seashore odour, 'a pure and rich sensation of smell.' In my own case olfactory dreams have been rare and insignificant.
Taste, as we usually understand it, really involves, as is well known, an element of smell, and taste dreams of this kind seem to occur from time to time under the influence of any slight disturbance of the mucous membrane of the mouth or slight indigestion. It is possible that the latter element was present in the following dream: I imagined that, following the example of a friend, I gave some cigarettes to a tramp we had casually met, and that, in return, we felt compelled to drink some raw gin he carried. I did so with some misgiving as to the possible results of drinking from a tramp's flask, but although in real life I had not tasted gin for many years, the hot burning taste of the spirit was very distinct. On awakening, my lips seemed hot and dry, and it was doubtless this labial sensation which led dream consciousness to seek a plausible explanation in cigarettes and spirits. Although the spirit seemed to have the specific flavour of gin, it is always difficult, if not impossible, in dream sensations, to distinguish between what one feels and what one merely concludes that one feels. In such a case, that is to say, it remains doubtful whether the labial sensation evokes the specific hallucination of gin, or whether it merely suggests to sleeping consciousness that the gin has been tasted, much as it is possible to suggest to the hypnotised person that the substance he is tasting is a quite different substance, that salt is sugar, or that water is wine.
As with dreams of smell, it is not always possible to detect any external stimulation as the cause for a taste or pseudo-taste dream.[66] This may be illustrated by a dream which belongs strictly to the tactile class; I dreamed that I called upon a medical acquaintance whose assistant I found in a dark surgery. I absently took up a broken medicine bottle and put it to my mouth, when my friend came in. I spoke to him on some medical topic, but he entered his carriage, and was driven off before he had time to answer me. I then found that my mouth was full of fragments of broken colourless glass, which I carefully removed. This dream was constructed, in the manner which has been often illustrated in the previous pages, of small separate incidents which had occurred during the immediately preceding days. One of the incidents was the fact that I had myself smashed a little coloured (not colourless) glass and carefully picked up the fragments. But the vividest part of the dream was the sensation of broken glass in the mouth, and on awaking no sensation could be detected in the mouth. So that though the most plausible explanation of such a dream would be the theory that the recent experience with broken glass had suggested to sleeping consciousness the explanation of an unpleasant sensation actually experienced in the mouth, there was nothing whatever to support that theory.
The falling of light on the closed eyes, or the half opening of the eyes, has been found to serve as a visual stimulus to dreams, but I have myself no decisive evidence on this point.[67] In the case of a lady who dreamed that a lover was in her room, and that suddenly the door opened, and she saw her mother standing before her with a bright light, which awoke her, she could find nothing in the room, no light, to account for the dream. It is, of course, unnecessary for a dream of a bright light to be actually produced by an external visual stimulus accompanying the dream, for the spontaneous retino-cerebral activity itself produces sensations of light. Thus, on the night after a pleasant walk in a country lane through which the setting sun shone, I dreamed that I was walking along a lane in which I saw a bright light and my own vast shadow in front of me. It would seem that, on the whole, the curtain of the eyelids effectually shuts out light from the eye during sleep, and that the sense which is more active during the day than any other is the most carefully guarded of all during the night. The peculiarly delicate and unstable nature of the chemical basis of vision makes up for this protection from external stimulation, and by its spontaneous activity ensures that even in dreams vision is the predominant sense.
What we find as regards the part played in dreams by excitations arising from the external specific senses holds good also for excitations arising from internal organic sensations. The main difference is that the stimuli which reach sleeping consciousness from the organs within the body—the stomach, heart, lungs, sexual apparatus, bladder, etc.—are usually more vague and massive, more difficult to recognise and identify, than are the more specific sensory stimuli which reach us from without. These visceral excitations may be transformed within the brain into imagery so unlike themselves that we may refuse to recognise them, and must frequently experience some amount of hesitation. Evidence of this fact will come before us in due course later on. I only wish to refer here to the more obvious part played in dreams by sensations arising within the body.
We should expect that the visceral processes to be translated most clearly and directly into dreaming consciousness would be, not those which are regular and continuous, but those which assert themselves, more or less imperiously, at intervals. This is actually the case. The heart, for instance, probably plays a part in dreams only when disturbed in its action, and even then nearly always a very transformed part. On the other hand, when the impulses of the generative system arise in sleep to manifest themselves in erotic dreams, the resulting imagery is usually very clear, and with very definite and recognisable sexual associations. Erotic dreams are, indeed, in both men and women, among the most vivid of all dreams, and the most emotionally potent.[68]
The bladder, again, is an internal organ which makes its functional needs felt only at intervals, and thus, when those needs occur during sleep, they become conscious in imagery which easily recalls the source of the stimulus. It may, indeed, be said that vesical dreams are full of instruction in the light they throw on the psychology of dreaming. This has long been well known to writers on dreams. Thus Scherner, many years ago, insisted on the interest and importance of vesical dreams. In women, especially, he regarded them as very frequent and developed, most dream stories of women, he considered, containing symbolic representations of this organic irritation. Water, in some form or another, is naturally the commonest symbol. In Scherner's opinion, also, all dreams of fish playing in the water are vesical dreams.[69]
In its simplest form the vesical dream is what Freud would term a wish-dream of infantile type, frequently in the magnified form common in dreams, and sometimes transferred from the dreamer himself to become objectified in another person, or even an inanimate object.[70] There is, however, a very important difference according to whether these dreams take place in an adult or in a young child. In the adult it almost invariably happens that the dream act remains merely a dream act, and no corresponding motor impulse is transmitted to the bladder. But when such dreams occur to very young children, in whose brains the motor inhibitory mechanism is not yet fully established, it not infrequently happens that the motor impulse is transmitted and the expulsive action of the bladder is set up in sympathy with the imagery of the dream; thus is established the condition known as nocturnal enuresis. As the young brain develops, and inhibition becomes more perfect, these vesical dreams cease to exert any actual effect on the bladder, even when, as sometimes happens, they continue to occur at intervals in adult life.[71] Occasionally, both in those who have and those who have not suffered from nocturnal enuresis in childhood (especially women), vesical dreams of this character may occur without even any real distension of the bladder. In some of these cases the dream can be shown to be due to a reminiscence or suggestion from the waking life of the previous day. Dreams stimulated by organic sensations from within are thus found to resemble those proceeding from sensory sensations from without in that they are both exactly simulated by dreams which are mainly of central origin.
When we turn to those internal organs of the body which normally carry on their functions in a constant and equable manner, seldom or never obtruding themselves into the sphere of consciousness, any disturbance of function seems much less likely to be translated into dream consciousness in a simple and direct form. It is sufficient to take the example of the heart. When the heart is acting normally any consciousness of its action is as rare asleep as awake. Even when cardiac action is disturbed, either by disease or by temporary excitement, dream consciousness seldom realises the physical cause of the disturbance. Occasionally, indeed, the cardiac disturbance may reach sleeping consciousness without any very remote transformation; thus a lady dreams that she is fainting while really breathing in a slightly laboured and spasmodic way; but at another period the same lady, at a time when she was suffering from some degree of heart weakness, dreamed one night, when the trouble was specially marked, that she was driving sweating horses up a steep hill, urging them on with the whip in order to avoid an express train which she imagined was behind her. This dream of sweating and panting horses climbing a hill has been noted by various observers to occur in connection with heart trouble.[72] The real difficulty of the panting and struggling heart instinctively finds its apparent explanation in a familiar spectacle of daily life.
In another case a dreamer awoke from a disturbed sleep associated with indigestion, having the impression that burglars were tramping upstairs, but immediately realised that the tramp of the burglars' feet was really the beating of her own heart. Somewhat similarly, when suffering from headache, I have dreamed of hammering nails into a floor, a theory obviously invented to account for the thump of throbbing arteries.