Mastication, Digestion and Assimilation. 15 



days. The stomach of the ox is never without considerable con- 

 tent, even after long starvation. The digestion of the starchy 

 matter of the food through action of the saliva continues in the 

 stomach. After the food 'enters the stomach a churning motion 

 is set up which causes it to travel from the place of entrance to- 

 ward the exit. While this motion is going on, a fluid is being 

 poured upon it from the lining of the stomach. This fluid is at 

 first alkaline, but gradually becomes more and more acid. 



The amount of gastric fluid poured out has not yet been defi- 

 nitely determined. Some writers place it as high as one-fourth 

 the weight of the body daily, others a tenth, and others even less. 

 The composition of the gastric fluid of the sheep is as follows: 



Water 986.14 



Organic matter (especially ferments) 4. 05 



Sodium chlorid 4.37 



Calcium chlorid 0. 11 



Hydrochloric acid 4.05 



Potassium chlorid 1.52 



Ammonium chlorid 0.47 



Calcium phosphate 1.18 



Magnesium phosphate 0.57 



Ferric phosphate 0.33 



The constituents of the gastric juice which effect changes are 

 pepsin, rennet and acid. Pepsin is a soluble ferment which acts 

 upon the food only in the presence of dilute acid. Rennet has 

 the power of curdling milk, one part coagulating 400,000 parts 

 of casein. Cane sugar is not fermentable and cannot be assimi- 

 lated until it is changed to glucose and laevulose. Hydrochloric 

 acid is present in considerable amount in the gastric juice. Cane 

 sugar in the food is slowly changed by this acid into laevulose 

 and glucose. The main action of the gastric juice is, however, 

 in converting the albuminoids into peptones, leaving the fatty 

 matter and cellulose to be attacked later. The stomach of the 

 horse is so small that it cannot contain a full feed at one time, 

 and consequently that portion which is first eaten is usually 

 pushed on from the stomach into the small intestines before it 

 has been long acted on by the gastric juice. 



