160 ELEMENTARY AGRICULTURAL CHEMISTRY 



chloric acid. The gastric juice of sheep contains about the 

 lower, that of the dog the higher of these amounts. 



The walls of the stomach move about when food is present, 

 and knead and incorporate it with gastric juice, producing a 

 pulpy mass known as chyme. In this process the proteids are 

 largely dissolved, being converted ultimately into amino- 

 acids, the fat is melted, and the cell walls of the fatty tissue 

 are removed. A certain amount of hydrolysis of starch (i.e., 

 conversion of this substance into sugar) also occurs in the 

 stomach. The chyme then passes into the intestines, the 

 secretion of which has an alkaline reaction. The acidity due 

 to the gastric juice is therefore neutralised, and the chyme 

 then receives the secretions of the pancreas and liver. 



Pancreatic juice is a viscid, alkaline liquid containing various 

 organic substances and inorganic salts. Its specific constituents, 

 however, are three enzymes: (1) a diastatic one, amylopsin, 

 acting rapidly upon starch and converting it into dextrin and 

 maltose; (2) a fat-splitting one, steapsin or pialyn, possessing 

 the power of decomposing fats into glycerol and free fatty 

 acids, at the same time emulsifying the unchanged fat ; and 

 (3) a proteolytic enzyme, trypsin, which resembles pepsin in 

 its properties, except that it works best in an alkaline liquid. 

 Pancreatic juice is thus capable of completing the work com- 

 menced by the saliva and the gastric juice, and, in addition, 

 has the power of bringing about the emulsification of the fat. 

 This latter process, however, is greatly aided by the bile, the 

 alkaline secretion of the liver. 



Bile is a reddish-yellow (in carnivorous animals) or green 

 (in herbivora) liquid, with an alkaline reaction and intensely 

 bitter taste. It contains alkaline salts of bile acids, bile 

 pigments, fats, soaps and mineral matter. The bile acids 

 are mainly glycocholic acid, CjgH^jNOg, and taurocholic acid, 

 CggH^.NOyS, and to these substances the bitter taste of bile 

 is mainly due. The bile pigments consist chiefly of hiliriLbin, 

 CjgHjgNgOj, a reddish-yellow substance, insoluble io water 



