474 PHYSIOLOGY CHAP. 



liy impressing specific sensations of contact, temperature, light, 

 tones or noises, etc., on the sleeper so as to furnish the materials 

 for the construction of different dreams. 



After many years of auto-observation, Hervey de Saint- 

 Denys (1867) succeeded in acquiring a full memory of his own 

 dreams, ;md collected a large number of tacts. He held memory 

 to he the prime element in dreams, and ascribed its importance 

 to the sensorial and physical elements, which often act in the 

 production of dreams independently of the will of the individual. 

 It is certain that a great proportion of dreams are founded on 

 the spontaneous recurrence of the records of the most important 

 and recent, or even remote, events that have occurred in the 

 waking state. 



According to this author, dreams are characterised by the 

 automatic development of a continuous chain of mnemonic 

 images (clichd souvenirs) which are stored up as the mental 

 heritage of the sleeper. Incidental extrinsic stimuli (sound, 

 light) may introduce an extraneous idea into the oueiric current, 

 which causes it to deviate. Attention and will may also intervene 

 in dreaming ; they are not necessarily suspended altogether 

 during sleep. He claims to be able to alter and guide the oneiric 

 current at will in given directions. By causing himself to be 

 waked a number of times during sleep, he convinced himself that 

 the vivacity and intensity of the images are always in ratio with 

 the depth of sleep; the more profound the slumber, the more 

 vivid and clear the oneiric images. This favours the theory that 

 sleep is always accompanied by dreams, but auto-observations of 

 Hervey de Saiut-I)enys on this point are completely opposed to 

 other far more numerous records. 



The method which might be termed experimental dreaming 

 has been attempted with scanty result by many authors, both in 

 healthy individuals and in pathological subjects hysterical and 

 epileptic. 



Mourly Void of Christiania (1896) covered one hand of a 

 healthy subject with a glove, or bound up one leg, immediately 

 before sleep. On waking, spontaneous or compulsory, he recorded 

 the patient's dreams, and proved that they not infrequently 

 originated in the state of the limbs. A student whose hand had 

 been gloved during the night dreamt that he saw a hand issuing 

 from an abdomen which had been opened, apparently for a 

 surgical operation. Mourly insisted on the fact that the visual 

 hallucinations, so common in dreams, may be incited by sensorial 

 excitations of another modality. Cutaneo-muscular stimuli are 

 of cardinal importance in promoting the visual hallucinations of 

 dreams. 



Stewart relates of a friend that having fallen asleep with a 

 hot bottle at his feet, he dreamed of a journey to the crater of 



