242 ELEMENTS OF GENERAL SCIENCE 



the bakery, and the grocery. For the purposes of this study 

 we must go deeper into the subject. Foods have a long and 

 interesting history before they reach the hands of the local 

 merchant. 



In the first pla^e, we already know that our food materials 

 are in general either plant or animal products, and since the 

 foods of animals are either plants or other animals which feed 

 upon plants, it is easy to trace all foods back to a plant origin. 

 For instance, whether we eat the corn ourselves or feed it to 

 the cattle and afterwards eat the meat, it is from the corn 

 plant that the food comes. 



Since the cultivated plants are used as food for us or our 

 animals, it may be said that the farmer is in fact engaged in 

 operating a food factory with cultivated plants as his machin- 

 ery. Our question as to the origin of the world's food now 

 becomes a question as to the kinds of materials which the 

 plants make and how they make them. 



There are a few mineral materials, such as salt, to which 

 these statements do not apply, but, with the exception of 

 water, they are not used in great quantities and are not 

 further discussed at this time. 



260. Composition of foods. In all our foods there are five 

 classes of compounds : carbohydrates, fats, proteins, mineral 

 salts, and water. The first three are of chief importance. 



The carbohydrates we already know from our study of the 

 manufacture of plant foods in green plants. This process, 

 photosynthesis, is the source of all the carbohydrates in our 

 food. The most common carbohydrates are starch and several 

 kinds of sugar. 



The fats, like the carbohydrates, contain carbon, hydrogen, 

 and oxygen, but in different proportions. Cottonseed oil and 

 olive oil are familiar examples. There is some oil to be found 

 in almost every plant. 



Proteins are the materials of which the living substance is 

 composed. They contain the same three simple substances as 



