41() SLEEP. [BOOK iv. 



a complication indicates that the explanation is, at present at 

 least, inadequate. 



The phenomena of sleep shew very clearly to how large an 

 extent an apparent automatism is the ultimate outcome of the 

 effects of antecedent stimulation. When we wish to go to sleep 

 we withdraw our automatic brain as much as possible from the 

 influence of all extrinsic stimuli. We lie down in order to relieve 

 the skeletal muscles and indeed the heart too, from the lain un- 

 entailed by the erect posture ; we put off the tight garments 

 which continually spur the skin ; we empty the bladder to avoid 

 the stimulus of its distension ; and we choose for sleep the night and 

 a quiet place, drawing the curtains, in order that our eyes may be 

 withdrawn from light and our ears from sounds. In this connec- 

 tion may be quoted the interesting case which is recorded of a lad 

 whose sensory tie with the external world was, from a complicated 

 anaesthesia, limited to that afforded by a single eye and a single 

 ear ; the lad could be sent to sleep at will, by closing the eye and 

 stopping the ear. 



981. The cycle of the day is however manifested in many 

 other ways than by the alternation of sleeping and waking, with 

 all the indirect effects of these two conditions. There is a diurnal 

 curve of temperature, apparently independent of all immediate 

 circumstances, the hereditary impress of a long and ancient sequence 

 of days and nights. Even the pulse, so sensitive to all bodily 

 changes, shews, running through all the immediate effects of the 

 changes of the minute and the hour, the working of a diurnal in- 

 fluence which cannot be accounted for by waking and sleeping, by 

 working and resting, by meals and abstinence between meals. And 

 the same may be said concerning the rhythm of respiration, and 

 the products of pulmonary, cutaneous and urinary excretion. There 

 seems to be a daily curve of bodily metabolism, which is not the 

 product of the day's events. Within the day we have the narrower 

 rhythm of the respiratory centre with the accompanying rise and 

 fall of activity in the vaso-motor centres. Arid lastly, there stands 

 out the fundamental fact of all bodily periodicity, that alternation of 

 the heart's systole and diastole which ceases only at death. Though, 

 as we have seen, the intermittent flow in the arteries is toned down 

 in the capillaries to an apparently continuous flow, still the con- 

 stantly repeated cycle of the cardiac shuttle must leave its mark 

 throughout the whole web of the body's life. Our means of inves- 

 tigation are, however, still too gross to permit us to track out its 

 influence. Still less are we at present in a position to say how far 

 the fundamental rhythm of the heart itself, that rhythm which is 

 influenced, but not created, by the changes of the body of which 

 it is the centre, is the result of cosmical changes, the reflection as 

 it were in little of the cycles of the universe, or how far it is the 

 outcome of the inherent vibrations of the molecules which make 

 up its substance. 



