l".l 1 



AN AMERICAN TEXT- BOOK OF PHYSIOLOGY. 



withdrawal of blood from it, the blood supplied to the brain being probably 

 ;ii the same time increased (see Fig. 123). 



Tins experiment shows that during sleep the nervous system is capable 

 of reactions which are not remembered in any way, but which naturally 

 form a feature of the condition intermediate between full consciousness and 

 deep slumber. 



The depth of sleep as determined by the strength of the stimulus necessary 

 to elicit an efficient response has been measured. The stimulus in these ex- 

 periments was the sound caused by the fall of a ball upon a plate, and the 

 measure was the height from which the ball must fall in order to produce a 

 sound loud enough to awaken a sleeping person. The results of the observa- 

 tions are shown in Fig. 124. 



Strength of Stimulus 



800 



700 

 600 

 500 

 400 



300 



200 



-A 



<> i 



100 



Hours 0.5 1.0 1.5 20 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 63 7.0 7.5 7.8 

 Pig. 124.— Curve illustrating the strength of an auditory stimulus (a ball falling from a height) neces- 

 sary to waken a sleeping person. The hours marked below. The tests were made at half-hour intervals. 

 The curve indicates that the distance through which the ball required to tie dropped increased during 



the first hour, and then diminished, at first very rapidly, then slowly (Kolsehiitter). 



It is seen from this that the period of deep slumber is short, less than two 

 hours; and is followed by a long period, that of an average night's rest, dur- 

 ing which a comparatively slight stimulus is sufficient to awaken. A some- 

 what different curve has been more recently obtained by Monninghoff and 

 Piesbergen. 1 



It is evident that the effectiveness of such a stimulus is, however, no 

 measure of the recuperative processes in the central system. Repair is by no 

 means accomplished during the interval of deep sleep, and experience has 

 shown, as in the case of persons undertaking to walk a thousand miles in one 

 thousand hours that although such an arrangement left the subject with two- 



1 Zeitschrift fiir Biologic, 1893, Bd. xix. 



