200 OF SLEEP. 



The influx of blood is diminished by its derivation 

 from the brain and congestion in other parts ; it is im- 

 peded by the pressure of foreign matter upon the brain, 

 whether from serous or purulent collections, from de-. 

 pression of fractured bones, &c. 



This diminution of, or impediment to, the flow of 

 blood to the brain, causes a deficiency of water in the 

 ventricles and a collapse of them, upon which that acute 

 and deep physiologist, David Hartley, whom we have 

 already praised, explains the various phenomena of 

 dreams.* Besides other phenomena which accord with 

 this explanation, is a very remarkable one which I 

 witnessed in a living person whose case was formerly 

 mentioned, that of the brain sinking whenever he was 

 asleep and swelling again with blood the moment he 

 awoke. 



This opinion is likewise strengthened by the produc- 

 tion of continued watchfulness from congestion of 

 blood in the head. 



323. The quantity of sleep depends much upon age, 

 constitution, temperament, &c. ; generally speaking, 

 much sleep is the attendant of weakness, as we find 

 in infants born prematurely and in superannuated per- 

 sons, and the very frequent source of fatuity and torpor. 



Stcph. Gallini at the end of his Saggio d'Osservazioni sit i intori progress* 

 della Fisica del Corpo Umano. Padua. 1792. 8vo. 



Mauduit, in Fourcroy, in the Mcdecinc Eclairee, &c. T. iv. p. 273. 



T. Chr. Reil, Functioncs Organn minima; Pcctiliarcs. Hal. 1794. 8vo. p. 108. 



L. H. Chr. Niemcycr, Materiality zur Erregungsthcoric. Getting. 1800. 

 8vo. p. 71. 



Troxlcy, Versitchc in dcr Orgnnischcn Physik. p. 435. 



Brandis, Pathologic, p. 534. 



# Observ. on Man. Vol. i. p. 48. 



