SLEEP. 



687 



equally injured by it ; in fact, being possessed 

 with the belief that they are not suffering 

 from the exertion, they frequently protract it 

 until a sudden and complete prostration gives 

 a fearful demonstration of the cumulative 

 effects of the injurious course in which they 

 have been persevering. Those, consequently, 

 who are earlier forced to give way, are fre- 

 quently capable of accomplishing more in the 

 end. 



In regard to the degree of protraction of 

 sleep which is consistent with a healthy state 

 of the system in other respects, it is difficult 

 to speak with certainty. Of the numerous 

 well-authenticated instances on record*, in 

 which sleep has been continuously prolonged 

 for many days or even weeks, it is enough 

 here to state that they cannot be regarded as 

 examples of natural sleep ; the state of such 

 persons being more closely allied to hysteric 

 coma. An unusual tendency to proper sleep 

 generally indicates a congested state of the 

 brain, tending to apoplexy ; and it has been 

 stated that apoplexy has been actually induced 

 by the experimental attempts to ascertain 

 how large a proportion of the diurnal cycle 

 might be spent in sleep. This effect may be 

 readily explained, if we regard it as a general 

 law of the capillary circulation, that its rate is 

 increased by functional activity, and diminished 

 by inactivity ; for whilst congestion of the 

 brain arising from other causes will tend to 

 produce sleep, through the augmented pres- 

 sure it occasions, mental inactivity, if en- 

 couraged and persisted in, will itself tend to 

 produce congestion. 



Thus, on either side, inattention to the 

 dictates of Nature in respect to the amount 

 of sleep required for the renovation of the 

 system, becomes a source of disease, and 

 should therefore be carefully avoided. 



DREAMING. 



We have hitherto spoken of sleep in its most 

 complete or profound form, that is, the state 

 of complete unconsciousness. But with the 

 absence of consciousness of external things, 

 there may be a state of mental activity, of which 

 we are more or less distinctly conscious at the 

 time, and of which our subsequent remem- 

 brance in the waking state also varies in com- 

 pleteness : the impression being sometimes vivid, 

 definite, and enduring; sometimes shadowy and 

 evanescent ; sometimes not amounting to more 

 than the feeling that we have dreamed ; and 

 sometimes not even this being preserved, not- 

 withstanding that there may be positive as- 

 surance that the sleep has been thus disturbed. 

 This state, known as dreaming, is one of the 

 highest interest to the psychologist; but the 

 limits imposed upon us forbid our doing more 

 than enumerate its leading phenomena. 



The chief feature of the state of dreaming 

 appears to be, that there is an entire absence of 

 voluntary control over the current of thought ; 

 so that the principle of suggestion one thought 



* Such, for example, as that of Samuel Chilton 

 (Phil. Trans., 1694), and that of Mary Lyall (Trans, 

 of Roy. Soc. ofEdinb., 1818). 



calling up another, according to the laws of asso- 

 ciation has unlimited operation. Sometimes 

 the train of thought thus carried on is remark- 

 ably consistent. We witness scenes that have 

 occurred during our waking hours, and seem 

 to hear, see, move, talk, and perform all the 

 actions of life. We may experience every 

 kind of mental emotion, and may even compare, 

 reason, judge, and will, during our sleep ; and 

 our reasoning processes have frequently a re- 

 markable clearness and completeness, the 

 data on which they are founded being sup- 

 posed to be accurate. This consistency is usu- 

 ally the greatest, when the mind simply takes 

 up a train of thought on which it had been 

 engaged during the waking hours, not long 

 previously ; and it may even happen that, in 

 consequence of the freedom from distraction 

 occasioned by the suspension of ordinary sen- 

 sations, the intellectual operations may be 

 carried on during sleep with uncommon vigour 

 and success. Thus, to name only two instances, 

 Condorcet saw, in his dreams, the final steps 

 of a difficult calculation, which had puzzled 

 him during the day ; and Condillac states that, 

 when engaged with his " Cours d'Etude," he 

 frequently developed and finished a subject in 

 his dreams, which he had broken off before 

 retiring to rest. 



The imagination, equally with the reasoning 

 processes, sometimes moves in a consistent 

 course. Thus, Dr. Good relates the case of a 

 friend who composed a little ode of about six 

 stanzas, and set the same to agreeable music, 

 in his sleep, the impression remaining so vividly 

 that he was able to write down both the words 

 and music on awaking in the morning ; and 

 Coleridge relates of himself that his fragment, 

 entitled " Kubla Khan," was composed during 

 sleep, which had come upon him whilst reading 

 the passage in " Purchas's Pilgrimage " on 

 which the poetical description is founded, and 

 was written down immediately on awaking. The 

 images, he says, " rose up before him as things, 

 with a parallel production of the correspondent 

 expressions, without any sensation or con- 

 sciousness of effort." It would seem ne- 

 cessary, in most cases of this kind, that the 

 results should be committed to paper imme- 

 diately on waking, before the train of thought, 

 continued from the dream, has been disturbed 

 by any other. Thus, Coleridge tells us that, 

 after having written for some little time, he 

 was interrupted by a person on business, who 

 continued with him above an hour; and on 

 the departure of his visitor, he found, to his 

 surprise and mortification, that "though he 

 still retained some vague and dim recollection 

 of the general purport of the vision, yet, with 

 the exception of some eight or ten scattered 

 lines and images, all the rest had passed away 

 like the images on the surface of a stream into 

 which a stone had been cast; but, alas ! without 

 the after-restoration of the latter." In other 

 cases, a strong general impression of what has 

 passed through the mind in sleep may remain 

 on waking, without power of recalling the par- 

 ticulars. This was the case in the well-known 

 instance of the musician Tartini, to whom the 



