222 Agricultural Chemistry. 



perature, maximum digestive action being manifested at about 

 38 C., the temperature of the body. Further, a certain degree 

 of acidity is essential for procuring the highest degree of effi- 

 ciency. Pepsin acts best in the presence of from 0.1 to 0.3 per 

 cent of free hydrochloric acid. It is said that the gastric juice 

 of the sheep has a low acidity, while that of the dog has the high- 

 est recorded among mammals. 



Chemically, the results are the same in the stomachs of all farm 

 animals, that is, the proteins are changed to the soluble forms 

 known as proteoses and peptones. The utilization of coarse fod- 

 der by the horse is not as complete as in the ox for the reason 

 that in the case of the former there is no preliminary remastica- 

 tion and trituration before the food material comes in contact 

 with the gastric juice. 



Another important function of gastric juice is that of curdling 

 milk, due to the presence in the secretion of the peculiar enzyme 

 known as rennin. This is present in the stomach of all mammal? 

 and it is the calf's active secretion, which is the source of com- 

 mercial rennet used in cheese making. The purpose of this 

 enzyme can only be conjectured. As the sole nutriment of the 

 young, milk occupies a peculiar position as a food stuff, and be- 

 ing a liquid, its protein constituents might easily escape complete 

 digestion were it to pass too hastily through the digestive tract. 

 Experiments have shown this to be true of liquid foods. But 

 when curdled by the rennin, the proteins of the milk in their 

 clotted state, must remain for a longer time in the stomach, and 

 their partial digestion by gastric juice made certain. 



Among other factors in gastric digestion, the muscular move- 

 ments of the stomach walls are to be emphasized, since we have 

 here a mechanical aid to digestion of no small moment and like- 

 wise a means of accomplishing the onward movement of the 

 stomach- con tents. From the stomach but little absorption of the 

 soluble food materials takes place. It is in the intestine that both 

 digestion and absorption are at their best. 



