in their actions. Whether, then, as a cause, or as a consequence, 

 where there is rhythmical action there must be corresponding rhyth- 

 mical waste and repair ; for we cannot reasonably suppose that the 

 heart, or any other similarly acting organ, has, as a special preroga- 

 tive, an exemption from the law of impairment in or by exercise : 

 such an exemption is, indeed, inconceivable. 



Now if rhythmic nutrition be thus proved as a necessary attend- 

 ant of rhythmic action, it must be regarded as the cause, not the 

 consequence, of the action ; for in all cases nutrition has precedence of 

 other actions in organized bodies ; and the time-regulation of nutrition 

 is a general and principal fact, and is a cause, not a consequence, of 

 many phenomena which we trace in other organs than the heart, 

 and many of which are attended with time-ordered movements. 



I suspect that, to many, that which will seem most difficult of 

 acceptance, is the belief that in so quick rhythmic actions as that of 

 the mammalian heart (for example), or that of cilia, there can be a 

 corresponding quickness of alternation of the progressive and retro- 

 gressive changes which essentially constitute nutrition. It must be 

 admitted that, when we watch these movements, they appear, at 

 first sight, very unlike anything that can result from nutritive 

 changes, in which we are apt to think of a certain deliberation and 

 quietness. But all rhythmic movements are not thus rapid ; and 

 when we watch the actions of a heart reduced to move only once in 

 two or three minutes (as a frog's may be by ligature around the 

 venous sinus), the appearance is like nothing more than it is like 

 that of a process of nutritive changes, in which the structures gra- 

 dually reach a climax of instability, and then quickly change. 

 Whatever value then there may be in the appearance of a rhythmic 

 action as an indication of its cause, it might be adduced on either 

 side of the inquiry. 



But let me add, that the nutritive changes to which I here refer, 

 do not involve the supposition of any rapidly successive making and 

 unmaking of the structures of the rhythmic organ, whether the heart 

 or any other. We have probably held too much of the making 

 and unmaking of elemental parts as essential to their maintenance 

 by nutrition. In the modelling of parts during development and 

 growth, such complete changes probably occur ; but in mere main- 

 tenance of parts there is no evidence of their frequent or ordinary 



