948 VARIOUS CIRCUMSTANCES THAT 



own thoughts, without being interesting enough 

 to maintain the activity of the brain. Sleep is 

 also induced by exposure to the air of a heated 

 room, which causes a determination of blood to 

 the surface, at the expense of the brain, muscles, 

 and other important organs. Hence it is, that the 

 most delightful of all soporifics is the warm bath, 

 especially after exposure to cold and fatigue, as 

 it removes the stiffness, soreness, and aching, 

 which sometimes prevent sleep when most re- 

 quired. But excessive warmth is unfavourable 

 to sound sleep ; first, by increasing the circula- 

 tion of blood through the brain ; and secondly, 

 by raising the temperature of the solids nearly to 

 an equilibrium with that of the arterial blood ; by 

 which the combination of its particles with the 

 solids is diminished. Hence it is, that when op- 

 pressed with too much covering, we feel languid 

 and unrefreshed on rising in the morning ; and 

 that men sleep more soundly in temperate than 

 in hot climates, where nothing more conduces 

 to healthful repose than cooling ablutions, or the 

 tepid bath, before going to bed. 



Whatever greatly diminishes the nutritive pro- 

 cess, tends to prevent natural sleep, which is 

 therefore always imperfect, if not wholly inter- 

 rupted during fever, and many other forms of 

 disease. It is also frequently prevented by over 

 activity of the nervous system, caused by mental 

 anxiety and too intense thinking, which interfere 

 with the nutritive process, and induce a feverish 



