154 HOW FOOD IS PREPARED FOR BODY USES 



Action of Gastric Juice. — If proteins are treated with artificial 

 gastric juice at the temperature of the body, they will become swol- 

 len and then gradually change to substances (peptones) which are 

 soluble in water. This is due to the action of the enzyme pepsin. 



The hydrochloric acid found in the gastric juice acts upon lime 

 and some other salts taken into the stomach with food, changing 

 them so that they may pass into the blood and eventually form 

 the mineral part of bone or other tissue. This acid also has a 

 decided antiseptic influence in preventing growth of bacteria, some 

 of which cause decay, while others cause disease. 



Experiments on Digestion in the Stomach. — Some very interest- 

 ing experiments have been made by Professor Cannon of Harvard 

 with reference to the movements of the stomach contents. Cats 

 were fed with a material having in it subnitrate of bismuth, a 

 harmless chemical that is visible under the fluoroscope. It was 

 found that shortly after food reached the stomach, a series of 

 waves began which sent the food toward the pyloric end of the 

 stomach. If the cat was feeling happy and well, these contrac- 

 tions continued regularly, but if the cat was cross or bad tempered, 

 the movements would stop. These experiments were repeated on 

 men, with like results, and show the importance of cheerfulness 

 at meals. Other experiments showed that food which was churned 

 into a soft mass was permitted to leave the stomach only when 

 it became thoroughly permeated by the gastric juice. It is the 

 acid in the partly digested food that causes the pyloric ring of 

 muscle to open and allow the food to escape little by little into the 

 small intestine. 



Position and Structure of the Pancreas. — The partly digested 

 food in the small intestine almost immediately comes in contact 

 with secretions from the liver, the pancreas, and the intestinal 

 glands. We shall first consider the function of the pancreas. The 

 pancreas is one of the most important digestive glands in the 

 human body. It is a rather diffuse structure, resembling the 

 salivary glands. Its duct (joined with the bile duct from the 

 liver) empties into the small intestine a short distance below 

 the pylorus. 



Work done by the Pancreas. — Starch paste added to artificial 

 pancreatic fluid and kept at blood heat is soon changed to sugar. 



