HORSE-BACK RIDING. 59 



apparatus that the phenomena peculiar to them are 

 subject to considerable exaggerations in order to sup- 

 ply the combustion rendered necessary by the con- 

 tractions, though in such cases assimilation is carried 

 on faster than the waste, and the muscle is better 

 nourished when active than when in repose. This 

 explains the development of the muscles under the 

 influence of exercise. 



The protean substances are not intended only to 

 supply the materials necessary for the renewal of the 

 tissues ; they do not penetrate to every part of the 

 vascular net-work ; a certain portion remains in the ves- 

 sels which has another destination. "The albumin- 

 ous aliments play a double action in the economy ; 

 when once introduced into the circulation, they divide 

 into two portions : one is assimilated and serves to 

 renew the tissues, and the other is burned with the 

 fatty and saccharine matters of the blood. These 

 internal combustions produce a reserve force which 

 furnishes the sensible heat necessary to maintain the 

 temperature of the body, and the heat which is 

 transformed into muscular power." (Gavarret.) 



The blood, which incessantly loses in the processes 

 of nutrition, combustion, and secretion, is regenerated 

 by the products of digestion which are being constantly 

 poured into its mass by the veins and the thoracic 

 canal, and the activity of nutrition therefore keeps 

 pace with that of digestion. 



The red globules play an important part in the 



