94 AHh DIGES 1 ION UK *OOD 



pleasing taste, and a savory odor. Gastric glands are also 

 stimulated by the presence of food in the stomach, but some 

 foods, such as soups and broths, stimulate greater activity than 

 other foods, such as cake and bread. A little warm soup at the 

 beginning of dinner is an aid to digestion because it starts an 

 abundant flow of gastric juice and assists the digestion of 

 heavier foods, such as vegetables, meats, and desserts. 



Gastric juice is slightly acid and its ferments act only in an 

 acid medium. Until the alkaline saliva sent to the stomach 

 from the mouth has been neutralized by the gastric juice, the 

 gastric ferments do not act. The larger the amount of saliva 

 swallowed the larger is the quantity of gastric juice secreted to 

 neutralize it, and hence the larger is the quantity of gastric 

 ferment present for the later digestion of protein. 



Pepsin and rennin, the gastric ferments, change the chemical 

 nature of proteins and transform them into substances usable 

 by the body; but they are powerless to bring about chemical 

 changes in starch and fats and hence digestion is not completed 

 in the stomach. 



Muscular movements of the stomach. The stomach is a 

 muscular bag or swelling of the alimentary canal, and, when 

 moderately full, holds about three pints. Its muscular walls 

 are constantly contracting and enlarging and by their move- 

 ments they mix every part of the food thoroughly with the 

 gastric juice. This constant agitation of the food with the 

 gastric juice soon reduces some of the food to a thick liquid mass. 

 As soon as sufficient of the liquid has been formed, the muscle 

 at the opening of the intestine relaxes and allows the escape of 

 the liquid into the intestine. The muscle then contracts and 

 closes the opening. In time more liquid food forms within 

 the stomach, the muscle again relaxes and allows food to escape 

 into the intestine. 



The stomach works best when it is moderately full. If it 





