EXPERIMENTS AND PRACTICAL WORK 79 



WHAT BECOMES OF OUR FOOD 



(See Tropical Readers, Book II, pp. 163-166.) 



Expt. 186. Flow of Saliva. Observe that as a bit of 

 bread or any food is chewed, saliva accumulates in the 

 mouth. 



Expt. 187. Saliva changes Starch into Sugar. Keep 

 some starch in the mouth for a little time, and observe 

 that it becomes sweetish to the taste. The change is 

 more easily noticed by putting a second lot of starch 

 in the mouth and observing the contrast. 



Expt. 188. Sweetbread. Obtain a "sweetbread" from 

 a butcher and make a drawing of it. 



Expt. 189. Diagram of Digestive Organs and Juices. 

 Copy the diagram of the digestive organs on page 164, 

 and show the position of the mouth, the gullet, the 

 stomach, and the intestines. In the diagram made by 

 you, show where the saliva, the gastric juice, the bile, 

 and the pancreatic juice meet the food in its course 

 through the body. 



THE AIR WE BREATHE 



(See Tropical Readers, Book II, pp. 166-169.) 



Expt. 190. Composition of the Atmosphere. Show 

 the presence of the following in the air: 



(a) Oxygen. Fan some smouldering coals, and note 

 that the fresh supply of oxygen thus brought to the 

 coals causes them to burn more brightly. 



(b) Nitrogen. Burn a small bit of phosphorus (less 

 than half the size of a red pea) under a bell jar standing 

 in water (fig. 31). Observe that the gas forms four- 

 fifths of the air, and by testing it with a lighted taper 



