The Digestive System. 163 



other changes in the tissue composing them. This causes 

 alterations in the saliva itself and accounts for the dryness 

 of the mouth so common among persons addicted to the 

 use of alcohol. 



Tobacco and the Salivary Glands. " The excessive 

 secretion of saliva induced by the use of tobacco is fol- 

 lowed by dryness of the mouth and throat, a natural result 

 of the overwork forced upon the salivary glands. This 

 dryness leads, in many persons, to the drinking of alcoholic 

 beverages."- Roger S. Tracy, M.D. 



Summary. i. The chief work of digestion is to make the food into 

 a liquid, ready to be absorbed and become part of the blood. 



2. The digestive system consists of a long tube, through which the 

 food passes, being subjected to mechanical and chemical processes. 



3. The parts of the digestive tube are the mouth, gullet, stomach, 

 and intestines. 



4. Along this tube are several large - glands, such as the salivary 

 glands, pancreas, and liver, which make liquids to pour upon the food. 



5. The tongue is composed of muscles, is very movable, and 

 (i) tastes the food; (2) keeps the food between the teeth during 

 chewing; (3) aids in swallowing. 



6. A tooth has crown, neck, and root. 



7. The tooth consists of dentine, containing a pulp cavity. The 

 crown is covered with enamel, and the root is covered with cement. 



8. There are thirty-two teeth in a full set, eight in each half jaw, 

 beginning at the front, two incisors, one canine, two bicuspids, and 

 three molars. The first set of twenty teeth are called " milk teeth." 



9. The teeth must be kept clean by brush and tooth powder. 



10. There are three pairs of salivary glands, parotid, submaxillary, 

 and sublingual. Their action is controlled by nerves. 



1 1 . The chief use of saliva is to change starch to sugar. 



Questions. i. Why should we not crack nuts with the teeth ? 



2. Why does the physician examine the tongue of his patient? 



3. Is it well to eat much soaked food ? Why not? 



4. How many teeth have you, and of what kinds? 

 5 Why is gum-chewing injurious ? 



