THE PRINCIPLES OF BIOLOGY 5 



afterward withdrawing the cardboard. Move the bottle 

 to the edge of the table and pass the lighted candle up 

 into it (Fig. 5). Does the flame go out as quickly as 

 in the former experiment ? 



If you breathe through a tube into clear lime water, 

 the water turns milky. The effect of the breath on the 

 candle and on the lime water shows that carbon dioxid is 

 continually leaving our bodies in the breath. 



FIG. 4. Breathing into a bottle.* FlG. 5. Testing the air in the bottle.i 



Oxidation and Deoxidation. The union of oxygen with 

 carbon and other substances, which occurs in fires and 

 in the bodies of animals, is called oxidation. The separa- 

 tion of the oxygen from carbon such as occurs in the 

 leaves of plants is called deoxidation. The first process 

 sets energy free,, the other process stores it up. Animals 

 give off carbon dioxid from their lungs or gills, and plants 

 give off oxygen from their leaves. But plants need some 

 energy in growing, so oxidation also occurs in plants, but 

 to a far less extent than in animals. At night, because 

 of the absence of sunlight, no deoxidation is taking place 



1 From Coleman's '* Physiology for Beginners," Macmillan Co., N.Y. 



