OF VITAL MOTION. 125 



that the heart is able to respond to the rhythmical 

 variations of force which can be pointed out as acting 

 upon the organ. On the other hand, the very reasons 

 which enable us to suppose that the heart may have 

 a rhythmical action, prevent us from expecting this 

 elsewhere. In other muscles, the more scanty supply 

 of blood-vessels argues a duller mobility, and the 

 absence of such marked variations in the contents of 

 these vessels the circulation in them being continuous 

 rather than intermittent argues also a feebler mani- 

 festation of the rhythmical variations of force In 

 other muscles, therefore, we have a feebler rhythm of 

 force, and a duller capacity of responding to this 

 rhythm ; and therefore the comparative absence of the 

 conditions which determine the rhythm of the heart 

 may be the reason why such a rhythm is absent else- 

 where. 



In conclusion: the heart is subject to the laws 

 which govern other mobile fabrics, and its history 

 would seem to offer no exception to what has gone 

 before. The systole refers to the common causes of 

 contraction; the diastole to the common causes of 

 dilatation. The rhythm also may be supposed to be 

 nothing more than the obedience of a natural suscep- 

 tibility to certain periodical variations in the supply 

 of intra-organic force, the existence of which variations 

 can be satisfactorily demonstrated. 



