36 HABIT AND INTELLIGENCE. [cHAP. 



partial or total suspension of communication between them 

 by tbeir nerve-fibres. 

 I This last expression may need explanation. Independ- 



ently of that lowering of the activity of the nervous centres 

 in which sleep consists, the fibres that connect them 

 appear, in particular cases, to cease to transmit any mes- 

 sages, or to keep up the communication. Thus, in the 



Reverie, state of reverie, the nerves of consciousness and thought 

 may be intently occupied with memory, reasoning, or 

 invention ; while the sensory and motor nerves, with their 

 ganglia, may be engaged with some consensual action, such 

 as the practice of some easy mechanical occupation ; but 

 the mind may have no consciousness of what the eye is 

 seeing, or what the hand is doing : in physiological lan- 

 guage, the currents of sensation that reach the sensory 

 ganglia excite no currents in the nerves of consciousness. 



Sleep. In sound sleep, the whole activity of the cerebrum 



appears to be suspended, including the nerves of con- 

 sciousness and will, as well as those of thought. The 

 activity of the sensory and motor ganglia is very much 

 lowered, though consensual actions are still possible, such 

 as turning round during sleep. 



Dreaming. Dreaming appears to be an intermediate state between 

 sound sleep and reverie. 



Somnam- The peculiarity of somnambulism appears to be that 

 ^' the action of the nerves of consciousness is suspended, 

 while all the rest of the nerves of mind are at work as in 

 the waking state. The actions of somnambulists show that 

 their senses must be awake, and capable of guiding con- 

 sensual action. Thought and wiU are also active, and yet 

 there is no consciousness. Somnambulism appears to be 

 the only mental state in which determinations of the will 

 are made unconsciously. It has been well remarked, that 

 dreaming and somnambulism are the opposites of each 

 other. In dreaming, the consciousness is partly awake, 

 though it is not in communication with the organs of 

 sense, and the other mental powers are asleep : in somnam- 

 bulism, the consciousness is asleep, and the other mental 

 powers are awake. 



