718 FUNCTIONS OF THE CEREBRO -SPINAL NERVOUS SYSTEM. 



his mind. He may even make a voluntary and successful effort to prolong 

 them if agreeable, or to dissipate them if unpleasing; thus evincing the pos- 

 session of a certain degree of that directing power, the entire want of which 

 is the characteristic of the true state of Dreaming. 



584. But the sensibility to external impressions may not be entirely sus- 

 pended in Dreaming ; and it is curious that even where sensations are not 

 recognized by the mind of the dreamer as proceeding from external objects, 

 they may affect the course of its own thoughts; so that the character of the 

 dreams may be in some degree predetermined by such an arrangement of 

 sensory impressions as is likely to modify them. This is especially the case 

 in regard to the dreamy state induced by certain narcotics, such as the 

 Hachisch (a preparation of Cannabis Indicci), employed for this purpose in 

 the East; for the emotional condition of the individual under its influence is 

 entirely under the control of external impressions ; so that those who give 

 themselves up to the intoxication of the fantasia, take care to withdraw 

 themselves from everything which could give their delirium a tendency to 

 melancholy, or excite in them anything else than feelings of pleasurable 

 enjoyment. 1 Moreover, there are certain forms of ordinary Dreaming, in 

 which the whole succession of thought and feeling (which is made manifest 

 by the words occasionally uttered, or by the play of countenance, or by the 

 more active movements of the dreamer) may be governed by external sug- 

 gestion ; as, for example, in the well-known case of the officer who amused 

 his friends by acting his dreams during the expedition to Louisburgh, the 

 course of these dreams being capable of direction by whispering into the 

 sleeper's ear, especially if this was done by a friend with whose voice he was 

 familiar. 2 Such forms of Dreaming constitute a transition to the state of 

 Somnambulism. 



585. Somnambulism. The phenomena of Somnambulism are so various, 

 that it is difficult to give any general definition that shall include the whole ; 

 but it is a condition which is common to all forms of this state, that the con- 

 trolling power of the Will over the current of thought is entirely suspended, 

 and that all the actions are directly prompted by the ideas which possess the 

 mind ; and the differences chiefly arise out of the mode in which the succes- 

 sion of ideas is directed, this being in some cases a coherent sequence through 

 the whole of which some one dominant impression may be traced, whilst in 

 other instances it is more or less completely determiuable by external sugges- 

 tions. These two forms are thus parallel to the states of spontaneous Ab- 

 straction and artificial Reverie (Electro-Biology) respectively; but differ 

 from them both in this essential feature, that they occur in a state of con- 

 sciousness so far distinct from the ordinary waking condition, as not to be 

 connected with it by the ordinary link of Memory ; and that although the 

 course of thought in Somnambulism usually manifests the directing influence 

 of previous habits, and the knowledge of persons and things possessed during 

 the waking state may be readily brought before the rnind, yet nothing which 

 occurs during the state of Somnambulism is ever retraced spontaneously, or 

 can be brought back by an act of recollection. Impressions upon the nervous 

 system, however, are sometimes left by strong emotional excitement, which 



1 See the Author's article, Sleep, in the Cyclop, of Anat. and Phys., vol. iv, pp. 

 688-690; and Moreau, Du Hachisch et de 1'AliemUion Mentale, Etudes Psycho- 

 logiques, p. 67. 



8 This case is detailed by Dr. Abcrcrombie (Inquiries concerning the Intellectual 

 Powers, 5th ed., p. 277), on the authority of Dr. Gregory, to whom it was related by 

 a gentleman who witnessed it. A case of a very similar nature, the subject of which 

 was a medical student at Edinburgh, is related in Smellie's Philosophy of Natural 

 History. 



