io Thaddeus L. Bolton and Eleonora T. Miller 



form a hierarchy, the lowest being perfectly rhythmical and auto- 

 matic, the highest are the least rhythmical, or, at least, their 

 rhythms are highly complex. Between the extremes of perfect 

 automatic action and occasional activity we find all degrees of 

 automatism. The heart centers, for instance, work most automat- 

 ically of all, and the centers controlling respiration only slightly 

 less. so. The centers controlling the movements of walking pos- 

 sess a still less automatic character. They may continue their 

 periodic activity for a number of hours with no change ; but the 

 time finally comes when the accumulated waste products within 

 them are so great and the degree of exhaustion falls so low as to 

 inhibit any further activity. They must then rest and recuper- 

 ate, after which it will be possible to act again. It is not too 

 much to say that they can continue in rhythmical activity for ten 

 or twelve hours, this often happening in case of forced marches, 

 when soldiers keep a uniform pace from morning until night 

 with scarcely a rest. Of course a long period of activity must 

 be followed by a correspondingly long period of rest in order 

 that the nerve centers may recuperate. For normal daily activity 

 of these centers the normal period of sleep is sufficient to restore 

 fully the nerve cells. The centers for the control of the arms 

 are less automatic than those that control the lower limbs. The 

 periods during which they can act -automatically are much 

 shorter, and rest and recuperation must come more frequently. 

 The normal period of sleep is not sufficient for the full recupera- 

 tion of arm centers, so that rests must be allowed during the 

 course of their daily activity. There are probably great indi- 

 vidual differences in this respect. Sailors and expert oarsmen 

 have been known to row continuously ten, twelve, and even 

 fifteen hours. The highest centers of the cerebral cortex seem 

 to show the smallest capacity for automatic activity. A center 

 which is active in the conscious perception of an object must 

 rest for a considerable time while another falls into activity in 

 the perception of a different object. Thus consciousness shifts 

 from one object to another, which means that the different cen- 

 ters act successively. Indeed, it is questionable whether a corti- 

 cal center ever acts in successive moments in exactly the same 



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