THE STORY OF THE HEART 73 



DOES THE HEART REST ? Oliver Wendell Holmes 

 in one of his poems, speaking of the work of the heart, 

 says : 



" No rest that throbbing slave may ask, 

 For ever quiv'ring o'er his task." 



This poetically expressed opinion, that of an anatom- 

 ist and physiologist by the way, is very far from the 

 truth. No organ of the body works perpetually. 

 Even if its action, as in the case of the liver, is more 

 or less of a continuous character, there are neverthe- 

 less periods during which the action is lessened and 

 slowed down, and in this way a period of comparative 

 rest is represented. In the case of the heart it may 

 be said that it rests practically as much as it works, 

 its periods of rest being equal to those of its activity. 

 It can be shown that if we suppose one single round 

 of the heart's work to be represented by a circle, an 

 accurate division of this circle would show that each 

 interval between the sounds corresponds exactly to 

 the sounds themselves in extent. The sounds we 

 have seen proceed in pairs. The first sound is 

 succeeded by a short pause, the second sound next 

 occurring. A longer pause exists between the second 

 and the next first sound representing the beginning 

 of the next pair of sounds. Measured accurately the 

 duration of the pauses equals the duration of the 

 sounds. Rest is therefore in the case of the heart 

 equal to work ; only the heart is in the position of a 

 workman whose duties enable him to take short spells 

 of rest between short spells of labour. The amount 

 of energy expended in the circulation of the blood by 

 the heart has been accurately measured. Knowing 

 the force which the heart exerts in a single round of 

 its duties it is a mere matter of multiplication to ar- 

 rive at an estimate of the amount of work performed 



