Respiration 



in which a burning coal was held, and like 

 that it contains carbonic acid gas. 



When once it has been used for respiration, 

 air, as we have seen, contains a harmful 

 substance, carbonic acid gas. This air is 

 henceforth unable to support life. An animal 

 which had nothing else to breathe would soon 

 perish. Nor is it able to maintain com- 

 bustion. This is quite clear, according to 

 the close resemblance between ordinary com- 

 bustion and the facts of life. Where the 

 animal can live, a lighted candle will burn ; 

 when the animal faints for lack of air, the 

 candle goes out. To know whether air is fit 

 to breathe we need only notice whether a 

 lighted candle will burn or go out. 



We will now collect our breath — that air 

 that has been working within us. This is a 

 very simple matter, as you will see. I take 

 a bottle with a wide mouth, fill it full of 

 water, cover the opening with the palm of 

 my hand and turn it upside down in a large 

 earthenware pan, also full of water. I hold 

 the bottle with one hand, taking care that the 

 mouth always remains under water. Then 

 we blow under the bottle with a reed. The 

 air issuing from the body disturbs the water 

 and rises in large bubbles through the 



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