298 THE INVISIBLE WORLD 



Nature sets her limit ^ of one per cent, of 

 the carbon poison is allowed, no more. Exceed 

 that limit, and the penalty is inevitable. To 

 breathe clean air is life. To breathe unclean air is 

 death. 



Outdoor air is the standard. Keep indoor air 

 up to the standard clean as the outdoor. Ven- 

 tilation will do it. At every point the pressure of 

 the atmosphere is about fifteen pounds to the 

 square inch. Open the window. That pressure 

 will push the outdoor air in, and keep pushing it 

 in, and pushing the bad air out, until the indoor 

 air is as clean as the outdoor air. 



As you value life, ventilate the living room. 



Ventilate the sleeping room. In a sleeping room 

 of usual size, absolutely air-tight, two persons, go- 

 ing to sleep at nine in the evening, would never 

 awake to see the sun rise suffocated, poisoned. 

 Open the window. In the coldest nights of winter, 

 open the window, and put on the extra blanket. 



Ventilate the schoolroom. In the ordinary 

 room, air-tight, sixty scholars spoil the air in six 

 minutes. The first duty of the teacher is to see 

 that every scholar breathes only clean air. Health 

 first; education next. 



Ventilate the church. In the usual church audi- 

 torium, air-tight, five hundred people would spoil 

 the air before the minister finishes prayer. Good 

 air first; prayer next. In bad air, the answer to 

 prayer is bad health. In good air, the answer is 

 good health. The best answer which could ever be 



