186 GENERAL SCIENCE 



has circulated through the body and is dark red. Because of the 

 large amount of carbon dioxide taken up, it passes through the 

 arteries to the lungs, where the carbon dioxide is given off into the 

 air sacs and expelled from the lungs into the air. The red cor- 

 puscles, after giving up the carbon dioxide, change to a bright red, 

 due to an enzyme (that acts like chlorophyll, the green coloring 

 matter of plants), which contains iron, and is the hemoglobin which 

 we have already mentioned. When it takes up oxygen it is known 

 as oxyhemoglobin. When the blood is light red the substance in 

 the red corpuscles is known as oxyhemoglobin, and when the blood 

 is dark red the substance in the red corpuscles is known as hemo- 

 globin, since it has lost its oxygen. 



Disposal of Carbon Dioxide in the Atmosphere. Countless 

 numbers of human beings, animals and fires are constantly giving 

 off carbon dioxide. Without some check, therefore, it would not 

 be long before the percentage of carbon dioxide in the atmosphere 

 would increase enormously. Nature has provided a wonderful way 

 to prevent the percentage of carbon dioxide from increasing to 

 over .03 per cent (.0003) or .04 per cent (.0004). 



The carbon dioxide of the atmosphere diffuses into the leaves 

 and stems of plants. In the leaves there is a green coloring matter 

 called chlorophyll. This chlorophyll absorbs certain light rays, and 

 the energy obtained is used by the plants in uniting the carbon 

 dioxide from the air with water which comes up from their roots 

 to form starch. Hence, the excess carbon dioxide of the atmosphere 

 is used up by plants in forming starch. This process of uniting'water 

 and carbon dioxide to form starch is called photosynthesis. (Photo 

 meaning light; synthesis to put together.) Thus the starch is really 

 manufactured by aid of the sunlight, through its agent chlorophyll. 



How Starch is Manufactured. All starch is composed of carbon, 

 hydrogen and oxygen. Starch is usually composed of: 



Six parts carbon (Co), 

 Ten parts hydrogen (Hio), 

 Five parts oxygen (65). 



Carbon dioxide and water, when put together by photosynthesis, 



