276 / ON SLEEP, DREAMING; 



of village bells at a distance, are all stimuli that produce no sensible ex- 

 haustion ; and, on this very account, form some of the most agreeable 

 images in nature. In like manner, the orbicular motion of the lips in a 

 sucking infant, is a source of so much comfort, and atteiided with so little 

 exhaustion, that virhether sleeping or waking, it will generally be found 

 mimicking the action of sucking, when at a distance from its nurse ; and, 

 perhaps, not thinking of such action itself. A person who, from habit, 

 has acquired a particular motion of any one of his limbs, a twirl of the 

 fingers, or a swinging of one leg over the other, perseveres in such motion 

 from habit alone, and feels no torpitude or exhaustion in the fibres that 

 are excited, although it might be intolerably fatiguing to another who has 

 never acquired the same custom. 



It is probable, then, that thought, and the action of the vital organs, 

 are of this precise character. We are totally ignorant, indeed, of the 

 mysterious mode by which either the one or the other was produced at 

 first ; but we see enough to convince us that the stimulus is, in both cases, 

 equally pleasing and gentle. And hence both actions continue without 

 exhausting us, except when unduly roused ; and form a habit too pertina- 

 cious to be broken through by any ordinary opposition. 



Thought, then, is to the sensory that which the motions I have just 

 spoken of are to the muscles which are the subjects of them. Both con- 

 tinue alike, whether we be reflecting upon the habit or not : but the habit 

 of thinking is so much older, and consequently so much deeper rooted than 

 that of any kind of muscular motion, except the muscular motion of the 

 vital organs, that it is impossible for us to subdue it by the utmost efforts 

 of the will : whence, like the action of the vital organs, it accompanies us, 

 not only at all times when awake, ^but in all ordinary cases during sleep, 

 and is the immediate and necessary cause of our dreaming. 



Thought can only be exercised upon perceptions introduced into the 

 sensory by the organs of external sense ; and hence the chief bent of our 

 thoughts must be derived, whether sleeping or waking, from the objects or 

 perceptions that most deeply impress us. The train of thoughts, then, that 

 recurs from habit alone, as in sleep or total retirement from the world, 

 must generally be of this description : in the former case, hovrever, by no 

 means correctly or perfectly ; because, there are others also which have a 

 tendency to recur, and neither the will or the senses are in action to regu- 

 late or repress them. Whence, as I have already observed, proceeds a 

 combination of thoughts or ideas, sometimes only in a small degree incon- 

 gruous, and at other times most wild and heterogeneous ; occasionally, 

 indeed, so fearful and extravagant as to stimulate the senses themselves 

 into a sudden renewal of their functions, and consequently to break off 

 abruptly the sleep into which they were thrown. 



Let us pursue this train of reasoning, and it will lead us to account, if 

 I mistake not, for some of the most extraordinary facts that are connected 

 with the recondite subject of sleep and dreaming. 



I have just observed that the stimulus of our ideas in dreaming is often 

 sufficient to rouse the external senses generally, and to awake us all of a 

 sudden. But this stimulus may also be of such a kind and just such a 

 streng(h, as to excite into their accustomed action the muscles of those 

 organs or members only which are more immediately connected with the 

 train of our dreams, or incoherent thoughts, while every other organ still 

 remains torpid. And hence, the muscles chiefly excited being those of 

 speech, some persons talk ; and others, the muscles chiefly excited beincf 



