4:54 NERVOUS SYSTEM. 



discuss the theory that sleep is attended with, or is produced 

 by, congestion of the cerebral vessels. 



The idea that the circulation in the brain is diminished 

 during sleep has long been entertained by cartain physiolo- 

 gists ; but until within a few years, it has rested chiefly upon 

 theoretical considerations. We find this view enunciated by 

 Blumenbach, in the following words : " These remote causes 

 may induce the proximate cause, which, upon mature con- 

 sideration, I think probably consists in a diminished or im- 

 peded flow of oxygenated (arterial) blood to the brain, for 

 that fluid is of the highest importance, during the waking 

 state, to the reaction of the sensorium upon the senses and 

 voluntary motions." This opinion was not entirely theo- 

 retical, as is seen by the following statement: "Besides 

 other phenomena which accord with this explanation, one is 

 very remarkable which I witnessed in a living person, and 

 has been already noticed that of the brain sinking when- 

 ever he was asleep, and swelling again with blood the mo- 

 ment he awoke." 1 



Passing over arguments by the older writers, for and 

 against this theory of sleep, we come to the researches of 

 Durham, in 1860, in which it w r as clearly demonstrated that 

 the supply of blood to the brain is always greatly diminished 

 during sleep. These experiments w^ere made upon dogs. 

 A piece of the skull, about the size of a shilling, was removed 

 with a trephine, and a w r atch-glass was accurately fitted to 

 the opening and cemented at the edges with Canada balsam. 

 "When the animals operated upon in this way were awake, 

 the vessels of the pia mater were seen moderately distended, 

 and the circulation was active ; but during perfectly natural 

 sleep, the brain retracted and became pale. " The contrast 

 between the appearances of the brain during its period of 

 functional activity, and during its state of repose or sleep was 

 most remarkable." 2 These observations were confirmed in 



1 BLUMENBACH, The Institutions of Physiology, Philadelphia, 1817, pp. 178, 179. 



2 DURHAM, The Physiology of Sleep. Guy's Hospital Report^ Third Series, 

 London, 1860, voL vi., p. 153, et seq. 



