4:56 NEKVOUS SYSTEM. 



without interfering with the current of blood, and such 

 experiments do not positively show whether the loss of sen- 

 sibility be due to pressure upon the nerves or upon the ves- 

 sels. 1 An important observation bearing upon this point is 

 the following, cited by Prof. Hammond : In a lady affected 

 with cirsoid aneurism of the scalp, both carotids were tied 

 at different times, one by the late Dr. J. Kearney Rogers, 

 and the other by Prof. "W. II. Yan Buren. " No peculiar 

 symptoms were observed in consequence of these operations, 

 except the supervention of persistent drowsiness, which was 

 especially well marked after the last operation, and which, 

 even now, is at times quite troublesome." The last opera- 

 tion was performed seven years ago. a The bearing of these 

 facts is sufficiently evident. They all go to show that the 

 supply of blood to the brain is very much 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 compressing the 

 veins, congestion is the result, and we have stupor or coma. 

 If diminished now of blood through the cerebral vessels 

 be the cause of natural sleep, it becomes important to inquire 

 how this condition of physiological anaemia is brought about. 

 It must be, that when the system requires sleep, the vessels 

 of the brain contract in obedience to a stimulus received 

 through the sympathetic system of nerves, diminishing the 



1 See page 256. 



2 HAMMOND, op. cit., p. 42. 



Ligation of both carotids, when the patient recovers from the operation, does 

 not always induce drowsiness, which is probably due to free collateral circulation, 

 by which, in some cases, the full supply of blood to the brain" is maintained. 

 In a remarkable case published by Mussey, both carotids were tied for aneu- 

 rism, one being operated upon about six weeks after the other. In this case, it 

 is remarked that " at no period subsequently to the operation of tying the 

 second carotid, with the exception of the faintness and debility which occurred 

 from the actual loss of blood on the removal of the tumor, has there been a 

 single symptom of deficiency of blood in the brain." (MUSSET, Case of Aneu- 

 nsm by Anastomosis, in which both the Primitive Carotid Arteries were tied. 

 American Journal of the Medical Sciences, Philadelphia, 1829, vol. v., p. 316.) 



