are, without knowing it, living among what from the waking point of view are called hallucinations. This process by which dreams are formed in sleeping consciousness through the splitting of the dreamer's personality for the construction of other personalities has been recognised ever since dreams began to be seriously studied. Maury referred to the scission of personality in dreams.[168] Delboeuf dealt with what he termed the altruising by the dreamer of part of his representations.[169] Foucault terms the same process personalisation.[170] Giessler attempts elaborately to explain the enigma of self-diremption--the formation of a secondary self--in dreams; if, he argues, a touch or other sensation exceeds the dream-body's capacity of adaptation--_i.e._, if the state of stimulus is above the apperceptive threshold--only one part of the perception is referred to the dream-body and the other is transferred to a secondary self.[171] This explanation, while it very fairly covers the presentative class of dreams, directly connected with sensory stimuli, cannot so easily be applied to the dramatisation of our representative dreams, which are not obviously traceable to direct bodily stimulation. The splitting up of personality is indeed a very pronounced and widely extended tendency of the mind, and has, during recent years, been elaborately studied. We thus have the basis of that psychic phenomenon which is variously termed secondary personality, double personality, duplex personality, multiple personality, alternation of personality, etc.,[172] and in earlier ages was regarded as due to possession by demons. Such conditions seem to be usually associated with hysteria. The essential fact about hysteria is, according to Janet, its lack of synthetising power, which is at the same time a lack of attention and of apperception, and has as its result a disintegration of the field of consciousness into mutually exclusive parts; that is to say, there is a process of dissociation. Now that is a condition resembling, as we have seen, the condition found in dreaming. It is not, therefore, difficult to accept the view of Sollier and others, that hysteria is a condition allied to sleep, a condition of vigilambulism in which the patients are often unable to obtain normal sleep, simply because they are all the time in a state of abnormal sleep; as one said to Sollier: 'I cannot sleep because I am asleep all the time.' It may thus be the case that hysterical multiple personalities[173] furnish a pathological analogue of that tendency to the dramatic objectivation of portions of our personality which is normal and healthy in dreams.