346 FOOD AND NUTRITION 



oxygen with the two most important elements found in foods, 

 viz., carbon and hydrogen, carbon dioxide and water are the 

 common products. 



Exercise 76. To Show that Water and Carbon Dioxide are Produced in 

 the Human Body 



(a) Blow the breath against a cold window pane or some other cold 

 surface and observe the film of moisture deposited. Where did the 

 water come from? In what state was it in the breath? In what 

 state is it now on the cold surface? What caused the change? 

 Much of the moisture expelled in the breath comes from the water 

 drunk, but a part also comes from the water formed in the body by 

 the combination of the hydrogen of foods with oxygen. 



(b) By means of a glass tube blow the exhaled breath through 

 clear lime water contained in a clean bottle. What happens to the 

 lime water? What substance does it show is present in the exhaled 

 breath (Ex. 25/) ? Now take a bottle filled with such air as you are 

 inhaling, place some clear limewater in the bottle, cover the mouth of 

 the bottle, and shake the liquid with the contained air. What happens 

 to the limewater? Can you detect any evidence of carbon dioxide in 

 this fresh air? Was carbon dioxide more abundant in the exhaled 

 breath than in the inhaled breath? Where did the extra amount 

 come from? 



380. Where Do the Foods Obtain Their Energy? It is a 

 notable fact that all energy-giving power of the foods of 

 animals and of the higher plants is traceable to the work of 

 green plants. Green plants are the only living things in all 

 the world that have the power to take up the non-nutritious 

 materials like water, carbon dioxide, and mineral matter and 

 build them into the nutritious foods like sugar, fat, and pro- 

 tein. If we eat the flesh of animals, we are still dependent 

 upon the green plant for our food, for the animal either got its 

 food from plants or from some other animal which subsisted on 

 plants. Sunlight is necessary for the growth of the green 

 plant. Sun energy is taken into the plant through the leaves 

 and is stored in the food made by the plant. Thus it is that 

 the green plants are the food factories of the world, gaining 

 their raw materials from the earth and the air, and storing in 

 the finished product the energy derived from the sun. 



