694 SLEEP. [BOOK iv. 



ence of all extrinsic stimuli ; and an interesting case is recorded of 

 a lad whose connection with the external world was, from a compli- 

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

 single ear, and who could be sent to sleep at will, by closing the 

 eye and stopping the ear. 



The cycle of the day is however manifested in many other ways 

 than by the alternation of sleeping and waking, with all the in- 

 direct effects of these two conditions. There is a diurnal curve of 

 temperature (see p. 468), 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. And 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. 



