DIGESTION IN THE STOMACH AND INTESTINES. 85 



formation. They are here mixed with the saliva, which 

 penetrates them thoroughly, softens and dissolves them in 

 part, and thus renders their mastication, taste, and degluti- 

 tion more easy. The saliva also transforms the amylaceous 

 substances contained in the food first into dextrine and then 

 into glycose or sugar; it reduces a portion of the fatty 

 bodies to an emulsion that is to say, it separates them into 

 particles held in suspension in the salivary fluid, and begins 

 the decomposition which is completed in the digestive canal. 



Digestion in the stomach. From the mouth the alimentary 

 mass descends through the pharynx and oesophagus to the 

 stomach, where it mingles with the gastric juice, one of the 

 most powerful agents of digestion. The gastric juice is 

 secreted by glandular tubes situated in the mucous mem- 

 brane of the stomach. It is a colourless fluid, saltish as well 

 as acid to the taste. It contains, among other elements, 

 alkaline chlorides, lactic acid, and an organic substance 

 called pepsine, which is peculiar to it. The gastric juice 

 pours into the stomach in considerable quantities when food 

 is introduced into it, mingles there with the mass, softens it, 

 and induces a fermentation which results in their ultimate 

 liquefaction. During digestion a characteristic movement 

 takes place in the stomach and intestinal canal the circular 

 fibres of the muscular membrane contract successively from 

 above downwards, and push the alimentary substances in the 

 same direction. Gradually as the lower fibres contract the 

 upper ones relax in order to contract anew. This is called 

 the peristaltic movement. Under its influence the contents of 

 the stomach are kept incessantly in motion, mixed with the 

 gastric juice, and directed toward \htpylorus. This orifice 

 is so named because it is like a door-keeper to the stomach, 

 allowing the aliments which have been sufficiently elaborated 

 to pass out while the others are retained in the organ. 

 After a time, which varies from three to five hours in dif- 

 ferent individuals and at different ages, the alimentary mass 

 is converted into a grayish paste, acid, and almost fluid; it 

 then takes the name of chyme, and the function of the 

 stomach, chymification, is accomplished. 



Intestinal digestion. In proportion as the chyme reaches 



