1 8 HORSE-BACK RIDING. 



jected to a motion communicated by a foreign body, 

 act, however, either to preserve certain attitudes or to 

 communicate motion to the machine or instrument 

 upon which he may be placed ; in a word, that cer- 

 tain parts of himself participate in the motion. 



To this class of exercises belongs horse-back riding, 

 for we have here two orders of movements, those 

 that the horse executes and those made by the rider 

 to keep himself in equilibrium on a movable base, 

 as well as to govern his animal. In other words, the 

 communicating force, the horse, and the active force, 

 the rider. 



But to appreciate fully the advantages of horse- 

 back riding, it is necessary to study first the local as 

 Avell as the general effects produced by active and 

 passive exercises. 



I. Effects of active exercises. — In order to form an 

 idea of the influence of active exercises on the econ- 

 omy, it is sufficient to examine the condition of the 

 members that are much exercised. 



If you set a part to work for a while, you see it 

 first swell from the afflux of a larger quantity of 

 blood ; the heat becomes greater there, and If you 

 repeat habitually the same movements, you see de- 

 velop in the part which executes them a greater per- 

 fection of action, an increase of nutrition and of 

 energy. 



It is not only the organs of active movements that 

 experience such effects. The nutritive functions be- 



