SLEEP. 611 



" The influx of blood," he continues, " is diminished by its 

 derivation from the brain and congestion in other parts; it is 

 impeded by the pressure of foreign matter upon the brain, 

 whether from serous or purulent collections, from depression of 

 fractured bones, &c." 



" Besides other phenomena which accord with this explan- 

 ation, especially those of hybernating mammalia 8 , is a very re- 

 markable 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 production 

 of continued watchfulness from congestion of blood in the 

 head." 



Now it is certain that the supply of arterial blood to every 

 part, and especially to the nervous system, is requisite to its 

 functions and its life, and that in proportion to the activity of a 

 part is the activity of its supply of arterial blood. Analogy, 

 therefore, renders it extremely probable that, during the in- 

 activity of sleep, the brain, having less occasion for arterial 

 blood, has a less vigorous circulation than during the waking 

 state ; and we know that whatever diminishes the ordinary de- 

 termination of blood to the brain, or impairs the movement of 

 the blood through it 4 , disposes to sleep. But, although this be 



L. H. Chr. Niemeyer, Materialien zur Erregungsthcorie. Getting. 1800. 

 8vo. p. 71. 



Troxler, Versuche in der Orgardschen Physik. p. 435. 



Brandis, Pathologie, p. 534." 



Cullen, Physiology, p. 124. sqq. 



Adelon, Physiol. t. ii. p. 292. sqq. 



Diet, des Sc. Med. t, xix. p. 348. sqq. 



Bourdon, Principes de Physiol. 1. 6. p. *785. sqq. 



s " v. c. Of the alpine marmot, of which Mangili treats in Reil's Archiv. 

 vol. viii. p. 466. sqq. 



1 As arterial blood when at rest acquires the venous character, and the slower 

 its motion the greater is its tendency to assume this character, it is evident that 

 in congestion of blood, by which is meant simply an unusual quantity of blood 

 in the vessels of a part, not flowing with its usual freedom, the part affected has 

 not its proper supply of perfectly arterial blood. Hence congestion in the head 

 must, even from this cause alone, produce drowsiness, to say nothing of the 

 effect of pressure on the cerebral substance. 



SS 3 



