HORSE -BACK RIDING. 55 



special influence upon the muscular fibre of the coats 

 of the stomach and the intestines. These viscera 

 may be considered as fairly suspended in the abdom- 

 inal cavity where they are barely held and limited 

 in their movements by the folds of the peritoneum. 

 Each shock from the horse shakes them and makes 

 them to roll as it were upon each other, and causes 

 the changes in the relations of the convolutions of 

 the intestines. These shocks and knocks and rub- 

 bings act as a mechanical excitant upon the muscular 

 fibre, which in consequence contracts with more 

 energy, preserving, however, the peculiar character 

 of the fibre-cells — that is, of contracting slowly and 

 successively ; the action of the fibre being increased 

 and the peristaltic contractions acquiring more power, 

 there results from it a more intimate mixture of 

 the juices and aliments in the stomach, a more per- 

 fect chymification of the food, and a more prompt 

 and complete absorption of matters already digested ; 

 and, lastly, all those which have as yet escaped the 

 process are brought into the portions of the intestines 

 where their metamorphosis is effected. The stomach 

 emptied of food calls for a new supply ; hunger re- 

 minds us of this need, while a sensation of weight in 

 the anal region precedes defecation, an act by which 

 the remnants of the preceding digestion are expelled, 

 in order to give place to a new portion of matter 

 which may have in part escaped the digestive process. 

 The contractions of the great intestines by accelerat- 



