104 THE WONDERFUL HOUSE THAT JACK HAS 



are giving off moisture called insensible perspiration, 

 because it is so small in amount we do not realize 

 that it is passing out, and the air usually takes it up 

 before enough collects to dampen the underclothing. 

 As perspiration contains poisonous substances that the 

 body needs to get rid of, it is important that the air 

 should not be too moist to absorb perspiration readily 

 from the body. One of the reasons we often feel un- 

 comfortable on hot summer days when the air is full 

 of moisture, or humidity, as it is commonly called, is 

 because the perspiration is not readily taken up by 

 the air. On this account, the body is disturbed, for 

 it is not being relieved of all its poisons in the usual 

 way. It is also very important that the air we breathe 

 should not be too dry, for in that condition it takes 

 up moisture that the tissues really need. This can be 

 easily told from the parched condition of our throats 

 when we have been long in a room that is heated by 

 furnace air not containing enough moisture. 



We are now ready to begin the interesting story of 

 how air aids our body building by bringing in the 

 necessary oxygen and carrying out the poisonous 

 carbonic acid gas. The first part of this story, the 

 passing of air through the nose and trachea, branching 

 off by way of the bronchial tubes and penetrating 

 into the very remotest air-cells of the lungs, can be 

 noticed at almost every breath. In the illustrations 

 the relative position of the trachea and lungs can 

 be seen. The appearance of the treelike bronchial 



