98 THE WONDERFUL HOUSE THAT JACK HAS 



without air. Which must we have the oftener ? Most 

 people eat three times a day. While the number 

 of breaths taken depends largely on how old a person is 

 and whether the body is active or at rest, the average 

 has been estimated at about eighteen a minute, one 

 thousand eighty an hour, or twenty-five thousand 

 nine hundred twenty a day ! Resting or working, 

 asleep or awake, a ceaseless tide of this wonderful 

 air is continually pouring in and out of our lungs. 

 As it is the material most needed by our bodies, we 

 should always have an abundance at hand and be 

 sure it is of the very best quality. 



But as air is so entirely different from other sub- 

 stances with which we have to deal, how can we in any 

 way regulate it ? Is it not an invisible, magical some- 

 thing that performs its work in a good-fairy-like 

 manner, whether we will or not ? If we lived out-of- 

 doors, like Arabs or Gypsies, the air would certainly 

 do its part in building our bodies as well as the very 

 best of good fairies. Many of our hours are spent 

 indoors, however, and so we should learn to keep the 

 indoor air in condition to do its best work for us. 



We have found that the building value of foods 

 depends upon the proportion of certain useful com- 

 ponents they contain. Strange as it may seem, 

 chemists have discovered that air, too, is made up of 

 several different components. They are agreed that 

 about four-fifths of air is a gas called nitrogen, a 

 little more than one-fifth is another gas called oxygen, 



