160 THE VITAL PROCESSES 



digestion, may be here summarized: They supply the 

 necessary force for masticating the food. They propel 

 the food through the canal. They mix the food with the 

 different juices. At certain places they partly or com- 

 pletely close the passage until a digestive process is com- 

 pleted. They may even cause a reverse movement of the 

 food, as in vomiting. All of the alimentary muscles, except 

 those around the mouth, are involuntary. Their work is 

 of the greatest importance. 



Other Purposes of the Digestive Organs. The digestive organs serve 

 other important purposes besides that of dissolving the foods. They 

 provide favorable conditions for passing the dissolved material into the 

 blood. They dispose of such portions of the foods as fail, in the di- 

 gestive processes, to be reduced to a liquid state. A considerable 

 amount of waste material is also separated from the blood by the glands 

 of digestion (especially the liver), and this is passed from the body with 

 the undigested portions of food. Then the food canal (stomach in 

 particular) is a means of holding, or storing, food which is awaiting the 

 processes of digestion. Considering the number of these purposes, the 

 digestive organs are remarkably simple, both in structure and in method 

 of operation. 



HYGIENE OF DIGESTION 



Many of the ills to which flesh is heir are due to im- 

 proper methods of taking food and are cured by observ- 

 ing the simple rules of eating. Habit plays a large part 

 in the process and children should, for this reason, be 

 taught early to eat properly. Since the majority of the 

 digestive processes are involuntary and the food, after being 

 swallowed, is practically beyond control, careful attention 

 must be given to the proper mastication of the food and 

 to such other phases of digestion as are under control. 



Necessity for Thorough Mastication. Mastication pre- 

 pares the food for the digestive processes which follow. 

 Unless the food has been properly masticated, the di- 



