68 



ANIMAL MECHANISM. 



We have formerly noticed in the circulation of the blood an 

 influence which regulates and increases the effective work of the 

 cardiac pump ; it depends on the elasticity of the arteries.* 

 In like manner, in hydraulic machines, man has recourse to the 

 employment of elastic reservoirs, to utilize more fully the work 

 of pumps, and to render uniform the movement of the liquid, 

 notwithstanding the intermittent character of the motive 

 power. This effect may be compared to that which we have 

 before remarked in the elast^'city of muscles. 



Dynamic energy of animated motors. — Animated motive 

 powers and machines are subject to the same estimation of 

 work ; it is the dynamic energy of the former as compared 

 with the latter. 



The production of external work corresponding to 75 kilo- 

 grammetres per second, has been called the horse-power , or, 

 in more general terms, the motive power of one horse, it being 

 supposed that one horse could develop the same amount of 

 w^ork. 



But animal motors cannot work incessantly, so that the 

 horse-power would represent at the end of the day a much 

 greater amount of work than the animal could have produced, 

 had it been employed as a motive force. 



Man is estimated much lower as to his dynamic energy, 

 {-^ of a horse-power), and yet, if we only require from the 

 muscular force of a man an effort of short duration, it will 

 furnish dynamic energy exceeding that of a horse -power. In 

 fact, the weight of a man is often more than 75 kilogrammes ; 

 each time that the body is raised to the height of a metre 

 per second, in mounting a staircase, the man has effected 

 during this second the work adequate to one horse-power. 

 And if, during several instants, he can give to his ascent the 

 speed of two metres per second, this man will have developed 

 the work of two horse-power. 



Thus, in our estimate of the work done by the greatest or 

 the smallest animals, we must consider it as a multiple or a 

 fraction of the ordinary measure of horse-power. 



* Physiologic m^dicale de la circulation du sang." 



