214 SCIENCE PROGRESS 



that it is in the veins of the splanchic area, whilst Howell ^ says 

 that it is in the vessels of the skin. The sleepiness of persons 

 exposed to great cold, as in balloons and on the top of high 

 mountains, belongs to this type ; the excessive withdrawal of 

 heat depresses the entire organism, the cardiac mechanism not 

 excepted. Relative cerebral anaemia is again the cause of the 

 sleepiness after a Turkish bath and after a full meal, when the 

 skin and the alimentary canal are respectively flushed with 

 blood. The sleepiness of a person who has suffered from severe 

 haemorrhage is circulatory in origin. Clearly the converse of 

 this is insomnia due to an abnormally rapid or powerful heart- 

 beat, a very familiar form. The sleeplessness of an excited 

 child and of the feverish patient is of this type. We may then 

 allude to these factors in sleep-production as " circulatory," 

 whether the diminution of cerebral circulation be the result of 

 cardiac enfeeblement or of a such a degree of vaso-dilatation 

 as to reduce the cerebral blood-pressure to that point at which 

 unconsciousness supervenes. 



The view of sleep advocated by Howell is a circulatory one. 

 He attributes the fall in cerebral blood-pressure to a cutaneous 

 vaso-dilatation due to fatigue of the vaso-motor centres, this 

 fatigue being periodic and normally occurring once in the 

 twenty-four hours. 



A second factor predisposing to sleep is unquestionably the 

 absence of stimulation of the sense-organs, which, of course, 

 ultimately means of the brain itself. The famous case of the 

 boy described by Striimpell,^ blind in one eye and deaf in one 

 ear, who could be put to sleep by having his seeing eye bandaged 

 and his hearing ear closed up, is an extreme example of the 

 onset of sleep as due to the cutting off of sensory stimuli. The 

 corresponding insomnia, that from the presence of sensory 

 stimulation— the unextinguished light, the railway whistles, the 

 neighbour's poultry — is too familiar to require more than 

 mention. The variety of insomnia belonging to this class with 

 which the physician has most frequently to deal is that arising 

 from pain which is but a form of excessive sensory stimula- 

 tion. The sleeplessness arising from cold feet is also a familiar 

 example of this type. The sleeplessness from the painful 

 sensations that are due to overworked muscles after too long 



• Journ. Expcr. Medicine, 1897, vol. ii. p. 313. 



* Deut. Archiv f. kliti. Medicin^ xxii. 



