O'SHEA — ASPECTS OF MENTAL ECONOMY. 



1G5 



in his vicinity would have little chance of escaping from ene- 

 mies lurking everywhere. And now, although man is quite safe 

 in an environment of any amount of racket, yet he has not fully 

 outgrown this old racial tendency to awareness in the presence of 

 noise. It is instructive in this connection to observe a little 

 child who in the earliest weeks trembles with fright at a loud 

 noise, and cannot sleep except in an atmosphere of quiet. 



The effect of noise upon a sleeping subject has been studied 

 by Lombard and others, 1 and the results are conclusive in show- 

 ing that even a slight disturbance causes a decrease in peripheral 

 blood supply, indicating that the blood is flowing in increasing 

 quantities toward the brain which tends to return to the waking 

 state. The charts which follow show this phenomenon. 



1 



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'"ini.i'i' 1 " 1 



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i g . 11. Plethysmography record from the arm of a person sleeping in the lab- 

 oratory. A fall in the curve indicates a decrease in the volume of the arm. The 

 curve is to be read in the direction of the arrow. 1, the night watchman en- 

 tering the laboratory ; 2, the watchman spoke ; 3, watchman went out. These 

 changes occurred without waking the subject. (Donaldson, op. cit., p. 289.) 



Fig. 12. — Record similar to that above. Change in the volume of the arm of 

 Sleeping subject, caused by the sound of a music box which was started at •• 

 (Donaldson, loc. cit.) 



The importance then of quiet while one is asleep cannot be too 

 greatly emphasized. There should be a "rest" law in every 

 house where students room, enacting that after a certain reason- 

 able hour absolute quiet shall prevail. Certain it is, at any rate, 



J See for instance, Angell and Thompson, op. cit., for a summary of results of 

 investigations. 



