The Digestive System. 



161 



Action of the Salivary Glands. The salivary glands 

 pour into the mouth a liquid which they make from 

 materials taken from the blood. In structure the gland 

 may be compared to a bunch of grapes, the grapes repre- 

 senting the little cavities, with a wall of cells that make 

 the saliva. From each of these cavities the liquid passes 

 into its duct, represented by the stem of a single grape ; 

 many of these unite to form the main duct, which corre- 

 sponds to the main stem. A thick network of capillaries 



Mucous Membrane 



Duct of Gland 



Secreting Cells 



Fig. 69. Diagram of a Salivary Gland. (After Landois and Stirling.) 



surrounds the gland ; the liquid part of the blood (plasma) 

 soaks out through the capillary walls and surrounds the 

 gland ; it is now called lymph ; from the lymph the gland 

 directly obtains its material. 



Nerve Control of Salivary Glands. The glands are 

 doubly dependent on nerve control: 



1. Through the nerve control of the muscles in the 

 walls of the arteries the amount of blood sent to the 

 glands is regulated. 



2. Nerves also go to the cells of the gland to control 

 their activity. When we taste, smell, see, or even when 

 we think of, some delicious food the mouth may "water," 



