THE DIGESTION OF FOOD 99 



saliva seems to be modified by the nature of the food 

 offered, dry materials stimulating the parotid gland and 

 moist foods only the submaxillary and sublingual. The 

 organic constituents of the saliva are the peculiar prod- 

 ucts of the secretory activity of the cells of the salivary 

 glands, and the water and inorganic salts are regarded 

 as the result of cell secretion. 



THE STOMACH 



When the food leaves the mouth, it passes down the 

 gullet (esophagus) into the stomach. The only modi- 

 fications it has suffered up to this point are its reduction 

 to a finer condition and a possible action of the mouth 

 ferment upon the starch. After the food is swallowed, 

 changes of another kind begin sooner or later. 



Before considering gastric digestion from a chemical 

 point of view, we should become acquainted with the 

 widely differing structure of the stomachs of the various 

 farm animals. Those of the ox and horse are greatly 

 unlike. The stomach of the ox, and of all other rumi- 

 nants, consists of four divisions or sacs, whereas with 

 the horse and pig it is made up of a single sac. 



137. The ruminant stomach. The ruminant stomach 

 is really quite a complicated affair, and the way in which 

 it disposes of the food is understood only after a careful 

 study of details. It has four divisions or sacs: the paunch, 

 honeycomb, many-plies, and rennet, or what the physi- 

 ologist has named the rumen, reticulum, omasum, and 

 abomasum. With the ox these cavities contain on the 

 average not far from twenty-five gallons, about nine- 

 tenths of this space belonging to the rumen (Fig. 2). 



138. Esophageal groove. A gutter or canal with 



