594 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1911. 



to increase rapidly on awaking. Brush and Fayerweather observed a 

 lowering of the pressure during the first five hours of sleep, followed 

 by an increase up to the time of waking. 



Externally you find at the approach of sleep, effects of a slackening 

 of the circulation ; sometimes the surface of the body becomes con- 

 gested, indicating the need of a loosening of the clothing. Mosso, then 

 Francois Franck, measured this expansion of the blood vessels near 

 the surface, and Howell, then Lehmann, observed that it increases 

 until the second hour of sleep, then diminishes until awaking. It 

 has been possible to note the conditions of the circulation in the 

 brain in subjects who have lost part of the skull, or on very } 7 oung 

 infants whose skull bones have not yet united. The first to make 

 this observation was Blumenbach in 1795. He had occasion to exam- 

 ine a young man 18 years old, who before the age of 5 had fallen 

 upon his forehead, sustaining a fracture of the skull, causing loss of part 

 of the bone. When Blumenbach saw it the wound was healed, but 

 one could feel an opening underneath; this was depressed during 

 sleep, diminishing when awake, and replaced by a bump during a 

 strain. Blumenbach concluded from this that there is less blood in 

 the brain during sleep. Durham made these observations on some 

 animals that were trepanned and chloroformed, and he noticed that 

 the arteries as well as the veins were less swollen during sleep. Ham- 

 mond confirmed these conclusions, and even before Durham, he had 

 watched a man whose brain was laid bare by a railroad accident, 

 and he saw the pressure of the brain diminish during sleep and rise 

 up when the man awoke. He found the same condition in young 

 infants. But the accuracy of these observations was doubted and 

 was disputed by various writers, and it was only the registering 

 experiments made by Mosso, Francois Franck, and Salathe that 

 settled the question. Salathe held that the fontanels of young infants 

 beat more strongly during sleep, indicating a diminution of pressure 

 within the skull. Francois Franck, in the case of an invalid stricken 

 with necrosis of the right parietal bone, observed the same move- 

 ments of the brain and the same diminution of pressure. Mosso at 

 last registered in several cases where the brain was accessible the 

 movements which take place during sleep; the pulse, regular and 

 uniform, was not so high as during wakefulness. Furthermore, 

 Brodmann has added to these observations that the act of going to 

 sleep is characterized by a sudden increase in the volume of the 

 brain, and waking up by a diminution in its size. 



These statements concerning anaemia of the brain and expansion 

 of the blood vessels of the extremities during sleep has led certain 

 writers to seek here an explanation for sleep. Five hundred years 

 before Christ, Alcmeon of Crotone said : ' ' Sleep comes from a flowing 

 back of the blood into the veins, and waking up is caused by its 



