BREATHING AND PURE AIR 5 



for lack of oxygen. Ever afterwards, in memory of that 

 terrible night, the room itself was called the Black Hole 

 of Calcutta. 



It is fortunate for us that air does not often get so bad 

 as that in any room. 



QUESTIONS 



1. How long can a man go without breathing? 



2. What difference is there between the air we breathe and the gas 

 we burn? 



3. Which gas in the air keeps us alive ? 



4. What would happen to us if we could get nothing but carbon 

 dioxid to breathe? 



5. What happened in the Black Hole of Calcutta? 



