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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 suf- 

 ficient 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 strength, 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 being those of locomotion, walk in their 

 sleep, without being conscious on their waking of any such occurrence. 



Whatever be the set of fibres that have chiefly become exhausted from the 

 labour or stimulus of the day, the rest, as I have already noticed, partake 

 of the torpitude from a habit of association ; exhausted in some degree, also, 

 themselves, by the share of sensorial power which, as from a common stock, 

 they have contributed towards the support of the debilitated organ. But it 

 sometimes happens, either from disease or peculiarity of constitution, that all 

 the organs of external sense do not associate in such action, or yield alike to 

 the general torpor of the frame: and that the auditory, the optical, or some 

 other sense continues awake or in vigour while all the other senses are be- 

 come inert ; as it does also that such particular sense, like the muscles of par- 

 ticular members, as observed just above, is awoke or restimulated into action 

 in the m.idst of the soundest sleep, by the peculiar force and bent of the dream, 

 while all the rest continue torpid. 



If the organ of external sense thus affected with wakefulness be that of 

 hearing, a phenomenon may occur which has often been noticed as far back, 

 indeed, as the times of the Greek and Roman poets, but which has never 

 hitherto, I believe, been satisfactorily explained ; the dreamer may in this 

 case hear a by-stander who speaks to him ; and if, from a cause above speci- 

 fied, he should also have happened to talk in his sleep, so as to give the by- 

 stander some clew into the train of thoughts of which his dream is composed, 

 a conversation may be maintained, and the by-stander, by dexterous manage- 

 ment, and the assumption of a character which he finds introduced into the 

 dream, may be able to draw from the dreamer the profoundest secrets of his 

 bosom ; the other senses of the dreamer, instead of hereby rousing to detect 

 the imposition, being plunged into a still deeper torpitude, from the demand 

 of an increased quantity of sensorial power to support the exhaustion which 

 the wakeful or active organ is, in consequence, sustaining. This, however, 

 is a case of rare occurrence, though it seems to have occurred occasionally. 



If the wakeful organ be that of sight, and the dreamer, from a cause just 

 adverted to, be accustomed to walk instead of to talk in his sleep, he will be able 

 to make his way towards any place to which the course of his dream may 

 direct him, with perfect ease, and without the smallest degree of danger. He 

 will see more or less distinctly, in proportion as the organ of sight is more or 

 less awake; yet from the increased exhaustion, and of course increased tor- 

 por of the other organs, in consequence of an increased demand of sensorial 

 power from the common stock to support the action of the sense and muscles 

 immediately engaged, every other sense must necessarily be thrown into a 

 deeper sleep, or torpor, than on any other occasion. Hence the ears will not be 

 roused even by a sound that might otherwise awake him ; he will be insensi- 

 ble, not only to a simple touch, but to a severe shaking of his limbs ; and may 

 even cough violently without being recalled from his dream. Having accom- 

 plished the object of his pursuit, he may safely return, even over the most 

 dangerous precipices, for he sees them distinctly, to his bed ; and the organ 

 of sight, being now quite exhausted, or there being no longer any occasion 

 for its use, may once more associate in the general torpor, an^ the dream take 

 a new turn and consist of a new combination of images. 



