SALIVARY GLANDS 363 



Demonstration 2. To show the use of digestion. 



In one thistle tube place some saliva mixed with starch paste. In 

 a second tube place some paste and water. Fasten membrane covers 

 over the thistle tubes, and wash carefully all starch or other material 

 on outside of tube. Then place the two thistle tubes, large end down, 

 in a beaker containing just enough warm water to cover the membrane 

 on the tubes. 



Next test some saliva with Fehling's solution. Is there any grape 

 sugar present? 



At the end of the laboratory period test the contents of the beaker 

 with iodine and with Fehling's solution. Was there any starch in the 

 water ? Was there any grape sugar ? How did it get into the beaker ? 



Salivary glands. We are all familiar with the substance called 

 saliva which acts as a lubricant in the mouth. Saliva is manu- 

 factured in the cells of three pairs of glands which empty into the 

 mouth, and which are called, according to their position, the 

 parotid (beside the ear), the submaxillary (under the jawbone), 

 and the sublingual (under the tongue). 



Self-Testing Exercise 



The glands necessary for digestion are the . . (1) (2), 



(3), (4), and (5). They secrete (6) 



that cause digestion of the (7). Starches are changed to 



(8) by enzymes in the (9) . Glands may be in the 



form of (10) or (11). Small (12) control 



the (13) cells and the blood (14) to them. 



PROBLEM II. WHAT IS THE STRUCTURE AND WORK OF 

 THE MOUTH CAVITY? 



Laboratory Exercise. Comparison of mouth of a frog and of a 

 man. Compare the. open mouth of the frog with the diagram. Do 

 the same studying of your own mouth. Can you find all structures 

 shown in the diagrams? 



In man the mouth cavity and the internal surface of the food 

 tube are lined with mucous membrane. The mucus secreted from 

 gland cells in this lining makes a smooth surface so that the food 

 can slip down easily. The roof of the mouth is formed by a plate 

 of bone called the hard palate, in front, and a softer continuation 



