478 



ANIMAL MECHANICS, 



Law of Refreshment. w In considering the Law of Fa« 

 tigue of muscles, an interesting question arises as to the 

 law by means of which the fatigued muscles are restored to a 

 condition in which they are able to resume work as before, 

 This law may be called the Law of Refreshment, and its in* 

 vestigation requires the solution of the following problem 

 At what rate does fresh arterial blood supplied to muscles 

 restore to them the power of again giving out work, of which 

 they have been deprived by fatigue ? 



In the case of the heart, we have a muscle that never 

 tires during life, and we may therefore assume that during 

 each cycle of work and rest, a supply of fresh arterial blood 

 Is given to the heart, sufficient to enable it to commence 

 again, quite refreshed, a second cycle, and so on for ever, or 

 gt least for eighty or ninety years of a long life, If we define 

 the Coefficient of Refreshment to be the work restored to the. 

 muscle in foot pounds per ounce per second, we obtain the 

 coefficient of the heart's refreshment from the following data, 

 already given (pp. 144-5), 



Work done by heart in one cycle, equal to 3 ounces lifted 

 <% 



through 9,9.2 feet = -j- x 9,9a ft, lbs, 



Assuming the heart to beat 72 times in one minute, th© 



work done by heart in one second = 23 x Jt * 9.92 ft, Ibg, 



The weight of the heart is 9.39 oz t 

 Hence, 



The work done by the heart per ounce per second is 



eqita] to 



7 a x |* Q>QB 



60 •* id * 9,39 



©.2377 ft, lb* 



This amount of work par ounce per second mutt be given 



