60 



SLKJlll' AND DIJKAMS. 



Almost all. animals I'oll up in this way, and especially in 

 cold woatlier. In fact, tlic more effectually we can l<c!i^p 

 olT any kind of sensation IVoiri. oui- l)odi(!,s, wlKilJiei- ron,i;li- 

 n(!ss, cold, oi- pressure, tlic mon) readily w(! sliall, sleep. 

 Then \v(^ t;'et the room as (^aiet as ])ossible, the stiller the 

 better, and we keep oat the light and close onr eyes. Plero 

 iigain our object is to keep impressions ol'F onr run'vous 

 systems. JJy these means we isolate ourselves from the 

 external world; the sights and sounds and manifold 

 sensatitms of the day are withdrawn, iind the only dis- 

 turbing causes are stimuli from within. These are chielly of 

 two kinds : (1) internal pain or discomfort, the action of 

 which in preventing sleep is obvious ; and (2) the activity 

 of the higher tiervous centres, especially our thoughts, 

 which act in much the same way as external stimuli. Each 

 thought, if vigorous enough, engondoi's others, and the mind 

 is kept in activity. This is not of itself, however, suflicient 

 to intei'fere with sleep if the brain be exhausted, unless 

 the ideas which pass through the mirui are very strong 

 or painful. The sleep of early childhood, when, thoughts 

 have not developed into tyrants, appears to bo never broken 

 by anything but bodily suffering. It is curiously regular, 

 " full of sweet dreams, and health, and qiiiet breathing." 

 Most people find by experience that it is important to 

 direct the current of thoughts into smooth, channels, and 

 as we cannot always control this current, there are many 

 devices for keeping it within bounds, such as counting or 

 repeating to one's self some monotonous sentence or idea ; 

 for example, the well-known story of the sheep going one 

 by one through a gate. Keats spoke of sleep as the "low 

 marmurer of tender lullabies," and anything with a slowly 

 alternating cadence or see-saw tune is very potent in ])ro- 

 ducing it, and monotonous sounds, such as falling I'ain or the 



