JIORSE-BACK RIDING. 35 



production of carbonic acid and water, and to these 

 may be added azote, urea, or uric acid — which are 

 derived from the complete or incomplete oxydization 

 of the quaternary substances ; and, lastly, heat is 

 engendered. The carbonic acid, the azote, the 

 water, urea and uric acid are carried away by the veins 

 which spring from the muscle and eliminated from 

 the circulation by the different emunctories of the sys- 

 tem ; but what becomes of the heat which is liber- 

 ated by this combustion ? The temperature of the 

 muscle in which these chemical transformations are 

 effected is raised, it is true, but this elevation of the 

 temperature is far from being in proportion to the 

 quantity of substance burned ; but a new phenome- 

 non is meanwhile produced : the muscle is con- 

 tracted. This contraction of the muscle is of the 

 greatest importance, since it balances a certain 

 weight — it represents the result of a process which 

 has absorbed the heat that has apparently disap- 

 peared, '' Thus, while the muscle acts, the heat 

 produced by the internal combustion divides itself 

 into two complementary parts. One appears as sen- 

 sible heat and regulates the temperature of the 

 muscle ; the other part, by the intervention of mus- 

 cular contractility, is converted into mechanical 

 force." 



These phenomena invariably succeed each other, 

 and they are the inevitable consequence one of the 

 other. The chemical action takes place first and 



