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

The liver secretes a digestive fluid called bile, which is an alkaline substance. Its chief purpose is to emulsify fats and to supply the alimentary tract with the requisite amount of moisture.

Fourth - The Pancreas

The pancreatic juice, secreted by the pancreas, is an alkaline and slightly acidulous substance. It contains three enzyms, the names and action of which are as follows:

Amylopsin completes the digestion of starch

Trypsin completes the digestion of pro-teids

Steapsin converts fats into fatty acids and glycerin

Fifth - The Small Intestines

The intestinal juices secreted by the small intestines are alkaline substances which change sugar and maltose into glucose, and perform the last step in the process of breaking up or subdividing food so fine that it will pass through the intestinal walls into the circulation.