FORMATION OF CARBONIC ACID IN THE BODY. 1 6$ 



matters leave charcoal when they are partly burned. 

 They must, therefore, contain carbon. It seems odd 

 that this should be so, and yet that they should not be 

 black ; but carbon is not always black. A diamond is 

 nearly pure carbon ; and can, by being heated, be changed 

 into ordinary black carbon, and then burnt and com- 

 bined with oxygen to make carbonic acid. Very few 

 substances which contain carbon combined with other 

 things, are black ; as, for example, carbonic-acid gas 

 itself, which is quite colorless. In our organs, the carbon 

 is all combined with other things; it only shows its black 

 color when the heat of the fire has separated them from it. 



As long as we live, our bodies are slowly burning or 

 oxidizing (Chap. VIII.). By this burning, carbonic acid 

 is produced from the carbon of their organs. When we 

 work hard, a great deal is made, and when we are at rest 

 much less. But even in deep sleep, oxidation is going 

 on inside our bodies all the time, to supply animal heat, 

 and force or power for every heart-beat, and each move- 

 ment of breathing. The carbonic acid produced by 

 oxidation in the body, must be removed. When it is 

 abundant, the organs cannot receive or use the oxygen 

 which they need in order to do their work. 



6. Breathing Air which contains much. Carbonic Acid, 

 will not Support Life. The more carbonic acid in the 

 air, the less oxygen. If there is very much carbonic 



leave when they are partly burned ? What must they, then, contain ? 

 Illustrate the fact that things containing carbon are not always black. 

 In what state does carbon exist in our bodies ? When does it show 

 its black color? What occurs as long as we live? What is produced 

 by the burning? Why is oxidation necessary even during deep 

 sleep? Why must the carbonic acid produced in the body be re- 

 moved ? 



6. How does the presence of carbonic acid in air affect the quan- 

 tity of oxygen ? What is the consequence to life if there is much of 



