94 HUMAN PHYSIOLOGY CHAP. 



4. The teeth are very important organs of digestion. They 

 are made of dentine covered with enamel on the crown, and 

 cement on the root. They are filled with connective tissue, 

 blood vessels, and nerves. 



5. There are twenty teeth in the first set and thirty- two in 

 the second. A tooth does not grow after it is once fully cut 

 and cannot repair itself; hence the teeth should be properly 

 cared for. 



6. The salivary glands pour from one to three pints of 

 saliva into the mouth daily, which serves to keep the mouth 

 moist, to dissolve some of the foods, and to change some of 

 the starches into sugars. 



7. Swallowing is accomplished by the proper action of a 

 large number of muscles. The food passes from the mouth 

 through the pharynx and oesophagus into the stomach. 



8. The stomach is the greatest enlargement of the digestive 

 canal and an important organ of proteid digestion. The gas- 

 tric juice comes from the innumerable gastric glands and con- 

 tains an acid and pepsin. The amount of gastric juice secreted 

 daily varies from ten to twenty pints. 



9. The stomach has three separate layers of muscles, which 

 enable it to contract in all directions and to thoroughly churn 

 the food. 



10. The time it takes to digest a meal depends upon the 

 amount and kind of food taken, the mode of cooking, the gen- 

 eral health of the person, and the kind and amount of exercise 

 taken. The food remains in the stomach from two to four hours. 



11. After the food has been properly changed in the 

 stomach it passes through the pylorus into the small intestine. 



12. The glands of the intestines, the pancreas, and the liver 

 all pour secretions into the intestines. 



13. The pancreatic juice is the most important digestive 

 fluid, for it can do all that the other juices do, and besides it 

 changes fats and oils into an emulsion, or into soap. 



