That the organic bodily sensations exert some influence on the formation of the dream is nowadays almost universally acknowledged, but the question as to the law underlying the relation between the two is answered in various ways and often in obscure terms. On the basis of the theory of bodily excitation the special task of dream interpretation is to trace back the content of a dream to the causative organic stimulus, and if we do not recognise the rules of interpretation advanced by Scherner,[58] we frequently find ourselves confronted with the awkward fact that the organic exciting source reveals itself in the content of the dream only. A certain agreement, however, is manifested in the interpretation of the various forms of dreams which have been designated as “typical” because they recur in so many persons with almost the same contents. Among these are the well-known dreams of falling from heights, of the falling out of teeth, of flying, and of embarrassment because of being naked or barely clad. This last dream is said to be caused simply by the perception felt in sleep that one has thrown off the bedcover and is exposed. The dream of the falling out of teeth is explained by “dental irritation,” which does not, however, of necessity imply a morbid state of excitation in the teeth. According to Strümpell,[66] the flying dream is the adequate picture used by the mind to interpret the sum of excitation emanating from the rising and sinking of the pulmonary lobes after the cutaneous sensation of the thorax has been reduced to insensibility. It is this latter circumstance that causes a sensation related to the conception of flying. Falling from a height in a dream is said to have its cause in the fact that when unconsciousness of the sensation of cutaneous pressure has set in, either an arm falls away from the body or a flexed knee is suddenly stretched out, causing the feeling of cutaneous pressure to return to consciousness, and the transition to consciousness embodies itself psychically as a dream of falling. (Strümpell, p. 118). The weakness of these plausible attempts at explanation evidently lies in the fact that without any further elucidation they allow this or that group of organic sensations to disappear from psychic perception or to obtrude themselves upon it until the constellation favourable for the explanation has been established. I shall, however, later have occasion to recur to typical dreams and to their origin. From comparison of a series of similar dreams, M. Simon[63] endeavoured to formulate certain rules for the influence of the organic sensations on the determination of the resulting dream. He says (p. 34): “If any organic apparatus, which during sleep normally participates in the expression of an affect, for any reason merges into the state of excitation to which it is usually aroused by that affect, the dream thus produced will contain presentations which fit the affect.”