SLEEP 621 



hereafter, it is unnecessary to discuss further 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 

 been entertained by some physiologists, but it has rested chiefly on theo- 

 retical considerations. The experiments of Durham (1860) seem to dem- 

 onstrate that the supply of blood to the brain is always greatly diminished 

 during sleep. These experiments were made on dogs. A piece of the 

 skull was removed with a trephine, and a watch glass was accurately 

 fitted to the opening and cemented at the edges with Canada balsam. 

 When the animals operated on were awake, the vessels of the pia mater 

 were seen moderately distended and the circulation was active ; but dur- 

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

 between the appearance of the brain during its period of functional 

 activity and during its state of repose or sleep was most remarkable." 

 There can hardly be a doubt, after these experiments, that during sleep 

 the cerebral circulation is considerably diminished in activity. 



The influence of diminished supply of blood to the brain has been 

 illustrated by compression of both carotid arteries. In an experiment 

 performed on his own person, Fleming produced immediate and pro- 

 found sleep in this way, and this result invariably followed in subse- 

 quent trials on himself and others. Waller produced anesthesia in 

 patients by pressure on both pneumogastric nerves ; but the nerves 

 are so near the carotid arteries that they could hardly -be compressed, 

 in the human subject, without interfering with the current of blood, and 

 such experiments do not positively show whether the loss of sensibility 

 be due to pressure on the nerves or on the vessels. In some rare 

 instances in which both carotid arteries have been tied in the human 

 subject, it has been stated that there is an unusual drowsiness following 

 the consequent diminution .in the activity of the cerebral circulation ; 

 but this result is by no means constant, and the morbid conditions 

 involved in so serious an operation usually are such as to interfere with 

 their value as facts bearing on the question under consideration. So 

 far as the human subject is concerned, the most important facts are 

 the results of compression of both carotids in healthy persons. These, 

 as well as experiments on animals, all go to show that the supply of 

 blood to the brain is diminished during natural sleep, and that sleep 

 may be induced by retarding the cerebral circulation by compressing 

 the vessels of supply. When the circulation is interfered with by com- 

 pressing the veins, congestion is the result, and there is stupor or coma. 



If diminished flow of blood through the cerebral vessels is the cause 

 of natural sleep, it becomes important to inquire how this condition of 

 physiological anemia is brought about. It must be that when the system 



