THE CEREBRUM, AND ITS FUNCTIONS. 821 



individual to be more attracted by the suspension of the sound than by its con- 

 tinuance ; or to the fact that the monotonous repetition of sensorial impressions is 

 often more favorable to sleep than their complete absence. Thus it is within the 

 experience of every one that the droning voice of a heavy reader on a dull sub- 

 ject is often a most effectual hypnotic; in like manner, the ripple of the calm 

 ocean on the shore, the sound of a distant waterfall, the rustling of foliage, 

 the hum of bees, and similar impressions upon the auditory sense, are usually 

 favorable to sleep ; and the muscular and tactile senses may be in like manner 

 affected by a uniform succession of gentle movements, as we see in the mode 

 in which the nurses " hush-off" infants, or in the practice of gently rubbing some 

 part of the body, which has been successfully employed by many who could not 

 otherwise compose themselves to sleep. The reading of a dull book acts in the 

 same mode through the visual sense ; for the eyes wander on from line to line 

 and from page to page, receiving a series of sensorial impressions which are 

 themselves of a very monotonous kind, and which only tend to keep the atten- 

 tion alive in proportion as they excite interesting ideas. In these and similar 

 cases, the influence of external impressions would seem to be exerted in with- 

 drawing the mind from the distinct consciousness of its own operations (the loss 

 of which is the transition-state into that of complete unconsciousness), and in 

 suspending the directing power of the Will. And this is the case even where 

 the attention is in the first instance voluntarily directed to them; as in some of the 

 plans which have been recommended for the induction of sleep, when there ex- 

 ists no spontaneous disposition to it. In other methods, the attention is fixed 

 upon some internal train of thought, which, when once set going, maybe carried 

 on automatically ; such as counting, or repeating a French, Latin, or Greek verb. 

 In either case, when the sensorial consciousness has been once steadily fixed, the 

 monotony of the impression (whether received from the Organs of Sense or 

 from the Cerebrum) tends to retain it there; so that the Will abandons, as it 

 were, all control over the operations of the mind, and allows it to yield itself up 

 to the soporific influence. This last method is peculiarly effectual, when the 

 restlessness is dependent upon some mental agitation, provided that the Will 

 has power to withdraw the thoughts from the exciting subject, and to reduce 

 them to the tranquillizing state of a mere mechanical repetition. 



842. The access of Sleep is sometimes quite sudden ; the individual passing 

 at once from a state of complete mental activity to one of entire torpor. More 

 generally, however, it is gradual ; and various intermediate phases may be de- 

 tected, some of which bear a close resemblance to the state of Reverie, whose 

 peculiar nature has been already described ( 824). The same ma} 7 be said with 

 regard to the transition from the state of Sleep to that of wakeful activity ; for 

 this also may be sudden and complete, although it usually consists of a succes- 

 sion of stages the complete consciousness of the individual's relation to the 

 external world, and the power of directing his thoughts and actions to any sub- 

 ject about which he may be required to exert himself, being the last to be ac- 

 quired. There maybe a rapid alternation of these different states; the loss and 

 recovery of the waking consciousness being many times repeated in the course 

 of a few minutes, when the circumstances are such as to prevent the access of 

 profound sleep by the recurrence of sensory impressions; as when a man on 

 horseback, wearied from want of rest, lapses at every moment into a dozing 

 state, from which the loss of the balance of his body as frequently and suddenly 

 arouses him; or when a man going to sleep in a sitting posture, gradually loses 

 the support of the muscles which keep his head erect, his head droops by degrees 

 and at last falls forwards on his chest, and the slight shock thence ensuing 

 partially arouses and restores his voluntary power, which again raises the head. 

 Similar fluctuations occur in the sensory perceptions; and these may be often 

 artificially induced by very simple means. "We find, for example, one condi- 



