Reverie, Somnambulism, Hypnotism, Sleep. 815 



sleep, leaving those awake upon which the stimulus is active. But after 

 awhile these may become exhausted and fall asleep, too. Often they re- 

 main, however, in a state of partial wakefulness, because when a person 

 is asleep under a droning hum or monotone, he will be likely to awake 

 upon its sudden cessation. 



It is in accordance with this same principle, that when a person has a 

 sense of fatigue from thinking steadily upon one subject, he is rested 

 by changing his thoughts to another. In the absence of a monotonous 

 sensory stimulus, a monotonous cerebral stimulus may often be substi- 

 tuted to induce sleep; for example, the persistent repetition of a formula 

 of words which does not call up active ideas, as the conjugation of a 

 verb, the recitation of very familiar verses, &c. 



Sounds and disturbances to which a person is habituated do not inter- 

 rupt sleep like those which are new, unless such disturbance is associ- 

 ated with a desire to be aroused. 



A person sleeping for the first time in a new place is apt to be aroused 

 by noises which do not disturb him after he is used to them. They are 

 stimuli not attended to, which provoke counteracting stimuli as shown at 

 the beginning of this chapter. 



The reduction during sleep of the amount of blood going to the brain 

 was shown by the experiments of Mr. A. Durham, on dogs. When he 

 removed (under chloroform) " a portion of the skull of a dog so as to 

 expose the cortical layer of the cerebrum, it was observed that as the 

 effects of the chloroform passed off, and the animal sank into a natural 

 sleep, the surface of the brain which had previously been turgid with 

 blood and inclined to rise into the opening through the bone, became 

 pale, and sank below its level. On the animal being roused, after a time, 

 a blush seemed to start over the surface of the brain which again rose 

 into the opening through the bone. And as the animal was more and 

 more excited, the brain substance became more and more turgid with 

 blood; numerous vessels which were invisible during the sleep being 

 now conspicuous, and those before visible being greatly distended. 

 After a short time the animal was fed, and when it again sank into re- 

 pose those vessels contracted again and the surface of the brain became 

 pale, as before." The retina has been examined during profound sleep 

 and found to be paler and its arteries more contracted than while the 

 subject was awake. 



Sleep is only one of several phenomena which depend upon a diminu- 

 tion of the supply of blood to the brain. A blow upon the head may, 

 in prize-ring parlance, put a man " to sleep;'' a fracture in which the 

 bone presses upon the brain preventing circulation, produces insensi- 

 bility. 



In Hysteric Coma, suspension of sensibility occurs suddenly, upon 



