160 ANATOMY AND PHYSIOLOGY. 



stricted ring then opens to let it through, and it passes into the 

 commencement of the bowels. But such is the delicacy of per- 

 ception with which the orifice of the stomach is endowed, that it 

 will not lefr undigested food pass, until it has been rolled about in 

 the stomach for many hours, and presented to it and rejected many 

 successive times. Indeed it often refuses to allow such food to pass 

 at all, and then there is no help for it but that it be ejected sum- 

 marily by vomiting. 



Let us now inquire into that part of the process of digestion 

 which goes on in the stomach. 



DIGESTION. 



In this organ the first of those changes takes place which fits the 

 extraneous matter swallowed as food, for being received into the 

 circulation of the fluids of the living body, and for becoming a 

 component part of the animal. For now, the gastric juice, acting 

 on the semifluid mass, quickly dissolves out the digestible part, and 

 entering into union with it, produces a new, thick, and turbid fluid, 

 which has been called chyme. The alimentary mass changes its 

 sensible and chemical properties, by an operation peculiarly animal, 

 or depending on the existence of life. The change is not strictly 

 chemical, for we do not find anything like it going on out of the 

 living body. An.imal or vegetable matters in any vessel possessing 

 the heat and moisture of the stomach, would quickly fall into fer- 

 mentation, and become sour, but the living properties of the stomach 

 prevent this. No acid is formed in the stomach in the healthy 

 state ; but when it is weak, and its nervous action is deranged, then 

 the symptoms which announce the diminished power are the extri- 

 cation of gas. and formation of acid, with oppression and uneasy 

 sensations. The contents of the stomach consist of air, partly 

 swallowed, partly formed in it, of the mucous secretion from its 

 coats, and of the chyme. The stomach having been stimulated by 

 fulness, by wind, and still more by the peculiar irritation of the 

 food undergoing digestion, the muscular coat is brought into action, 

 and the contents of the stomach delivered into the commencement 

 of the small intestine (duodenum). 



HUNGER. 



We are solicited to take food by the uneasy sensation of hunger, 

 a sense which appears placed as a safeguard lest the body should be 

 permitted to wear out. In the artificial state of society in which 



