HORSE-BACK RIDING. 57 



cording as the exercise is taken before or after eat- 

 ing. 



In fact, if we ride when the stomach is empty, or 

 nearly so — for the organ is never absolutely in a state 

 of vacuity — the intestinal digestion is materially slack- 

 ened, and the exercise would hasten the transformation 

 and absorption of the substances which might be in 

 the stomach intestine, and induce hunger. But if we 

 ride immediately after eating, the diaphragm and the 

 abdominal muscles would compress the intestines and 

 the stomach, and might induce vomiting, or at least 

 regurgitation, while at the end of an hour or two the 

 fulness of the stomach would be relieved and no incon- 

 venience felt. 



6. Nutrition. — The nutrition of the individual, the 

 consequence, nay, more, the object of all the other 

 functions which we have examined, is at once the 

 cause and the effect of all the physiological functions. 

 The impairment of any one of them reacts upon this 

 as the execution of the functions depends upon ana- 

 tomical elements. 



The blood which circulates in the vessels is the 

 agent of all nutrition. It is composed of two parts : 

 the one fluid, the plasma, containing the albuminoid 

 substances, the products of digestion ; this alone is 

 capable of traversing the walls of the capillaries, and 

 placing itself in direct contact with the tissues ; the 

 other is solid, in the form of globules, and, by reason 

 of its bulk, could not pass through the vessels : both 



