34 HORSE-BACK RIDING. 



others and which is the point of departure — that is, 

 muscular contraction. 



I. Muscular contraction. — The will commands, the 

 muscle obeys and contracts. What is the agent of 

 that contraction ? No one doubts the contractile 

 property of muscular fibre, but it is powerless with- 

 out the intervention of an external influence, upon 

 the nature of which physiologists have long disputed ; 

 some giving to nervous excitation an importance 

 which it certainly does not deserve, w^hile others 

 make the blood play an exaggerated part. 



All our present knowledge of this subject is ad- 

 mirably summed up in Gavarret's excellent work, 

 '' Les Phenomenes Physiques de la Vie. " According 

 to the learned professor, the closest possible con- 

 nection exists between contractibility and the phe- 

 nomena of combustion which takes place in the 

 network of the capillaries of the muscles. In fact, 

 when a muscular contraction is to be produced, the 

 nervous action is confined, so to speak, simply to giv- 

 ing an impulsion to the muscle, thus preparing it for 

 the action of another agent, the blood. The arterial 

 blood flows into and abundantly fills the capillaries 

 which permeate the muscle. The oxygen which it 

 contains burns with fresh energy the combustible 

 materials which it carries ; these are the products of 

 digestion, fatty and saccharine matter chiefly, with 

 some of the proteine substances. 



The result of these internal combustions is the 



