540 POPULAR SCIENCE MONTHLY. 



we have just defined are found in observations, now old, made by 

 Azam, Dufay, and other physicians. These observations are to- 

 day well known and trite. They have been published and ana- 

 lyzed in a number of medical journals, and even in some literary 

 ones. 



The state of somnambulism is artificially induced in hypno- 

 tism, which may be brought about in a large variety of ways, in 

 all of which there are reasons for supposing the psychological 

 causes play the larger part. When one now comes to define som- 

 nambulism from the psychological point of view he sees at once 

 that it constitutes a new mode of mental existence. The old mes- 

 merists were quite right when they described it as a second per- 

 sonality. 



Two fundamental elements constitute personality memory 

 and character. In the latter respect, as to character, induced 

 somnambulism is not perhaps always clearly distinguishable 

 from the waking state. It frequently happens that the somnam- 

 bulist does not relinquish the character that he had before he 

 was put to sleep. The reasons are manifold. This does not, how- 

 ever, hold for the second element of personality memory. It has 

 long been said that memory supplies the chief sign by which the 

 new state may be distinguished from the normal state. The som- 

 nambulist shows, in fact, a curious modification in the range of 

 his memory; the same regular phenomena of amnesia may be 

 produced in him as occur in the spontaneous variations of per- 

 sonality. 



Two propositions sum up the principal modifications of 

 memory which accompany induced hypnotic somnambulism ; 

 first, the subject recalls during his waking state none of the 

 events which happened during somnambulism ; and second, on 

 the other hand, when put in the somnambulistic state he may 

 remember not only the previous somnambulistic states, but also 

 events belonging to his waking state. It follows that memory 

 attains its maximum extent in somnambulism, since it then 

 embraces two psychological existences at once, as the normal 

 memory never does. It may even be remarked that the somnam- 

 bulist, when he endeavors to recollect certain particulars, has 

 better memory than the same person awake. Gurney has shown, 

 moreover, from studies of hysterical patients, that somnambu- 

 listic states may persist in the waking life; that the somnambu- 

 listic ego, the second condition, is not always completely effaced 

 when the waking state returns, but survives, coexists with normal 

 thought, and gives rise to complex phenomena of division of con- 

 sciousness. 



A second form of the phenomenon of double personality is the 

 coexistence of the two egos, which is presented in two cases. The 



