DIGESTION 17 



constitution of their molecules. That sounds difficult. 

 But when we know that composition and constitution 

 mean simply how a substance is made up or of what 

 it is composed, and that molecules are the smallest 

 parts of a substance, it does not seem so hard to 

 understand. 



Without consulting a dictionary, we can tell 

 the three different forms of matter, solids, liquids, 

 and gases. We know how sugar when heated turns 

 to sirup, how ice and snow change to water, how heat 

 turns water to steam, and how cold causes steam to 

 change back to water. We have seen yeast cause 

 the bread dough to rise, and heat make oatmeal expand. 

 In fact, hundreds of simple experiments will show 

 that material things are made up of different parts; 

 and that these parts can easily be made to separate 

 from one another and rearrange themselves in some 

 other form, if just the right process is used. 



The passage in the body through which food travels 

 while it is being changed into body building material 

 is called the alimentary canal. This wonderful pas- 

 sage is about thirty feet long. Its parts in order 

 from the mouth are the pharynx, esophagus, stomach, 

 small intestine, and large intestine. At various sta- 

 tions along this remarkable canal are situated small 

 chemical shops called glands. In these are secreted 

 fluids that help dissolve food, and change it into such 

 form that it may be absorbed into the blood and 

 become useful building material. 



