1869.] Notices of Scientijk Worhs. 401 



SLEEP.* 



The " physical basis of sleep," as some of our modern biologists 

 would perhaps be disposed to call the physiological phenomena 

 which attend that mysterious condition of the higher animals, is 

 admirably treated in the little work before us ; and we cannot do 

 better than draw attention to its suggestive pages, as we believe 

 a close study of the subject will throw fresh light upon those 

 psychical powers of man concerning which so little is kno^vu and so 

 much has been written. 



In the first portion of his work the author explains the physio- 

 logical cause of sleep with great clearness, and his theory appears to 

 be borne out by our present knowledge of the subject. Popularly 

 described, it is this : The brain is the organ of thought ; when the 

 brain is working, waste proceeds ; when that waste has continued 

 for some time, reparation is necessary ; full vessels and a rapid cir- 

 culation favour expenditure of the tissue, and a feebler and smaller 

 current conduces to repair.f When the activity of the brain lessens, 

 or when by a voluntary act it ceases, the diminution of the circu- 

 lation is effected through the increased activity of the sympathetic 

 ganglia which partially close the arteries that supply the brain, 

 and put a stop to the physiological action which is necessary for 

 the exercise of the mental powers. To facilitate the inactivity of 

 the mind which is necessary to give rest and reparation to the brain, 

 all the external avenues to the senses are closed, and so the mind is 

 no longer disturbed by sensory activities, and is turned inwards, so 

 to speak, upon itself only. 



In sound sleep, then, it is to be presumed that little or no 

 cerebral waste is going on, and when the reparation is complete we 

 awake in the natural order of events. The author tells us that 

 there are numerous causes of awakening, but they may " all be 

 reduced to one ultimate action, namely, revoking the force of the 

 ganglia upon the arteries, and reopening the arterial current 

 throughout the brain." % 



Many interesting phenomena connected with the sleeping state 

 are ably discussed by the author. He treats of the entire absence 

 of the power of hearing in some exhausted sleepers, as for example, 

 the wearied soldier whose slumbers are not disturbed by the roar of 

 cannon, so powerful is the hold of the sympathetic ganglia over the 

 brain in sleep. Also of somnambulism, where certain senses are 

 quite inactive and certain phases of the mind at rest, whilst others 

 are wide awake : — " Some awakening of thought, consciousness, and 

 will, recovered tactile sensibility, control over the muscles of the 



* ' On Going to Sleep.' By Charles H. Moore : Eobert Hardwicke. 



t The uutlior id hero quoting Mr. A. E. Durham ou the ' Thysiology of Sleep.' 



t 1'. 57. 



