( 87 ) 



who in J895 defeiulcd the tliesis that the inten-iiption of ('(nitju-t is 

 caused by retraction of the eii<l-arl)orisatioiis of tiie iieiira. 



This retraction of the eiid-arhorisations iiowever lias never yet 

 been observed, and might be, if occnrring, a consequence of sleep, 

 but the investigations of Apathy and Betiie (1894), wiio hohl tiiat 

 the tibrils of different neura pass into one anotiier, have rendered it 

 probable that the causation of sleej) is not to be found in this domain. 

 By the ildrd theory the origin of sleep is ascribed to the efïect of 

 so-called fiitigue-substances, which are presumed to be produced by 

 different functions during the waking state. 



Injections of lacteal acid, the sole known fatigue-substance, mean- 

 while offered only a negative result, moreover this theorj- is not 

 quite in accordance with the facts : 



l^''^. Because during sleep principally such functions are disturlxMl 

 as are dependent on momentaneous stimuli, i. e. the psychical func- 

 tions, whilst other functions dependent on stimuli (nutrition etc.) 

 received during the waking state, e.g. respiration, heart-movement, 

 secretion of sweat and urine, digestion etc., are influenced in a lesser 

 degree and may be brought likewise to decreased intensity by repose 

 without sleep. 



2"^. Because the want of sleep and the duration of sleep are 

 neither of them adequate to the performed psychical and physical 

 labour. 



3i'^. Because sleep may be interrupted at any time by a strong 

 stimulus, the functions operating immediately afterwards in a perfectly 

 normal manner. 



4'^'. Because among psychical functions those, originating partly 

 in preceding stimuli, still remain possible (dreams). 



5*'^ Because in the case of a new-born bal)e the want of sleei» 

 and the dui'ation of slee^) l)Oth diiitlnlsli with ificrcd.süK/ functions. 



The insufficiency of these different theories about the origin of 

 sleep ha\e led the physiologist Leonard Hill to the conclusion: the 

 causation of sleep must still be regarded as metaphysical ^). 



Meanwhile pljysiological psychology had taught us that the wakino- 

 state is consequent on the coiuluctiou of stimuli from the sui-rouud- 

 ings to the central nervous system, and as regai-ds man to the 

 psychical centra, a fad in pei-fect accordance \\\\\\ the experience 

 that tiie originating of sleep is favoured by darkness, monotonous 

 sounds and silence. The famous experiment of Stkimpki.l *), who 



1) The Lancet ISIK). I. p. ^28."). 



2) DciUches Arcliiv. fur Klin. Medicin. 1878 No. 22. 



