DIGESTION 



mous supply of a substance is called a gland. All 

 mucous membranes contain enough mucous glands to 

 keep their surfaces moist. In addition some mucous 

 membranes also contain glands which produce other sub- 

 stances. 



25. Salivary glands. Upon the sides of the mouth are 

 the openings of several small tubes through which a fluid 

 called the saliva is always enter- 

 ing to moisten the mouth. While 



one is eating, more saliva flows, 

 so that Qver a quart is produced 

 each day. Each tube runs deep 

 into the cheeks and suddenly 

 divides again and again like the 

 branches of a tree, so that the 

 finest tubes cannot be seen with- 

 out a microscope. Each tube 

 is made of cells set edge to edge. 

 These cells produce the aliva_ 

 from th^ Moor! 



Each bunch of tubes is rolled 

 together, forming a mass about the size of a walnut. Each 

 mass is called a salivary gland. There is a salivary gland 

 in front of each ear, and two under each side of the jaw. 

 In mumps these glands swell and produce lumps around 

 the lower jaw. 



26. The saliva. The saliva is a watery fluid which 

 flows very freely when anything is chewed. Saliva has a 

 little power to change starch to sugar, but its main use is 

 to dissolve the food into a thin paste which can be swal- 

 lowed. The food should always be chewed so long as any 

 lumps can be felt. 



27. The pharynx and swallowing. When the food has 



A salivary gland ( X 200). 



a tube of epithelium forming the 

 gland, cut lengthwise. 



b tubes cut crosswise. 



c connective tissue binding the 

 tubes in place. 



