554 DIGESTION. 



wrought on the food in the mouth. 4thly. Deglutition, or the part 

 taken by the pharynx and resophagus in digestion. 5thly. Chymifica- 

 tion, or the action of the stomach on the food. 6thly. The action of 

 the small intestine. Tthly. The action of the large intestine. And, 

 Sthly. Defecation or the expulsion of the fseces. All these processes are 

 not equally concerned in the formation of chyle. It is separated in the 

 small intestine: the first six, therefore, belong to it; the remainder 

 relate only to the excrementitious part of the food. The digestion of 

 solid food requires all the eight processes: that of liquids is more simple; 

 comprising only thirst, prehension, deglutition, the action of the stomach, 

 and that of the small intestine. Fluid rarely reaches the large intestine. 

 In inquiring into this important and interesting function, we shall first 

 attend to the digestion of solids, and afterwards to that of liquids. 



4. DIGESTION OF SOLID FOOD. 



a. Hunger. 



Hunger is an internal sensation, the seat of which is invariably refer- 

 red to the stomach. Like every internal sensation, it proceeds from 

 changes in the very texture of the organ. It is not produced by any 

 external cause; and to it are applicable all those observations, that were 

 made on internal sensations in general. In its slightest condition, it is 

 merely an appetite, (opst^; Germ. E s s 1 u s t;) but if this be not heeded, 

 the painful sensation of hunger (Fames, TU^OJ), supervenes, which 

 becomes more and more acute and lacerating unless food is taken. If 

 this be the case, however, the uneasiness gradually abates ; and if suffi- 

 cient be eaten, a feeling of satiety is produced. The sensation usually 

 occurs, in the healthy state, after the stomach has been for some time 

 empty, having finished the digestion of substances taken in at the previous 

 meal. Habit has a great effect in regulating this recurrence ; the appe- 

 tite always appearing about the time at which the stomach has been 

 accustomed to receive food. This artificial desire may be checked by 

 various causes; by the exciting or depressing passions, the sight of a 

 disgusting object, or anything that occasions intense mental emotion; 

 or it may be appeased by filling the stomach with substances that con- 

 tain no nutritious properties. As, however, the feeling of true hunger 

 arises from the wants of the system, the natural and instinctive sensa- 

 tion soon appears, and cannot be long postponed by any of these means. 

 Hence, it has been proposed to make a distinction between appetite and 

 hunger; applying the former term to the artificial, the latter to the 

 natural, desire. In these respects, there is certainly a wide distinction 

 between them, as well as in the capriciousness, which occasionally cha- 

 racterizes the former, and gives rise to singular and fantastic preferences. 



The sensation of hunger varies in intensity according to different 

 circumstances. It is more powerful in the child and youth than in one 

 who has attained his full height. In the period of second childhood, it 

 is urgent, probably owing to the diminished power of assimilation 

 requiring that more aliment should be received into the stomach. In 

 disease, the sensation is generally suppressed, and its place often sup- 

 plied by loathing or disgust for food: at times, again, its intensity makes 



