THEORIES OF SLEEP. 455 



the most satisfactory manner by Prof. Hammond, who, in 

 1854, noted the changes in the circulation during sleep in a 

 man who had a large opening in The skull from a railroad- 

 accident. These observations were made independently of 

 those of Durham, but were not published until some time 

 after. 1 Prof. Hammond cites numerous observations illus- 

 trating the diminished circulation in the brain during sleep, 

 in the human subject, which it is unnecessary to refer to in 

 detail, and this fact may now be considered as definitively 

 settled. 3 He also devised an instrument for measuring the 

 extent of the cerebral pressure. This instrument consists of 

 a brass tube, which is screwed into an opening made in the 

 skull, and is connected with a small glass tube filled with 

 colored water. The lower end of the brass tube is covered 

 with a thin sheet of rubber, which rests on the brain, the 

 cerebral pressure being marked by the height of the liquid 

 in the glass tube. In experiments made with this apparatus, 

 Prof. Hammond fully confirmed the results of his previous 

 observations. 8 



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, Dr. Fleming 

 produced immediate and profound sleep in this way, and 

 this result invariably .followed in subsequent trials upon 

 himself and others. 4 We have already alluded to the obser- 

 vations of "Waller, who produced anaesthesia in patients by 

 pressure upon both pneumogastric nerves ; but, as we then 

 remarked, the nerves are so near the carotid arteries that 

 they could hardly be compressed, in the human subject, 



1 HAMMOND, Sleep audits Derangements, Philadelphia, 1869, p. 37, et seq. 



' 2 An interesting case of exposure of the brain in the human subject i& re- 

 ported by Dr. Brown (American Journal of the Medical Sciences, New Series, 

 Philadelphia, 1860, vol. si., p. 400). 



3 HAMMOND, op. cit., Appendix. 



4 FLEMING, Note on the Induction of Sleep and Anaesthesia by Compression of 

 the Carotids. British and Foreign Medico-Chirurgical Review, London, 1855, voL 

 XV., p. 529. 



