[LESSON V]
CHEMISTRY OF DIGESTION
DIGESTIVE ORGANS AND DIGESTIVE JUICES
First—THE MOUTH:
The three salivary glands of the mouth secrete the saliva, which is an alkaline substance containing a digestive enzym called ptyalin.
The saliva begins the digestion of starch and moistens food to facilitate swallowing.
Second—THE STOMACH:
The gastric juice secreted by the mucous lining of the stomach is an acid. It contains hydrochloric acid and pepsin, which act on proteids, changing them to proteoses ("intermediate products formed naturally in the process of digestion") and peptone.
The gastric juice also contains rennet, which acts directly on milk, and indirectly on all proteids.
Third—THE LIVER: