20 HORSE-BACK RIDIXG. 



That increase of nutrition is, besides, a consequence 

 of the greater activity of the principal visceral func- 

 tions. 



But it is specially in the muscular system that is 

 manifested in the most remarkable manner that 

 activity of nutrition; for the muscles acquire more 

 volume, more density, more power, and in turn react 

 upon the internal organs. 



Active exercise practised in early life appears also 

 to increase the nutrition of the osseous system. The 

 muscular contractions develop the whole frame and 

 increase the size of the eminences where the muscles 

 are attached. To the muscular development is 

 always joined that of the circulatory system, and 

 from the well-being of the two apparatuses results a 

 robust constitution, and one ordinarily exempt from 

 infirmities. 



To resume, then, active exercises exert first their 

 influence on the muscles which execute the move- 

 ments, and they increase afterwards the action and 

 the energy of the assimilating organs, because the 

 muscles requiring from these a greater amount of 

 material proper to their development, double neces- 

 sarily their work, and because they communicate also 

 to the organs of nutrition agitations favorable to the 

 execution of their functions and to the nutrition of 

 tissue. 



2. Effects of passive exereises. — These exercises take 

 place without contraction of the muscles ; the body, 



