12.  Plants purify the air by removing the carbonic-acid gas.

13.  Alcohol and tobacco injure the blood corpuscles so that they cannot take up the oxygen from the air which the lungs receive.

CHAPTER XIV.

HOW TO KEEP THE LUNGS HEALTHY.

1.  Pure Air Necessary.—­A person may go without eating for a month, or without drinking for several days, and still live; but a strong man will die in a few moments if deprived of air.  It is very important that we breathe plenty of pure air.  There are many ways in which the air becomes impure.

2.  Bad Odors.—­Anything which rots or decays will in so doing produce an unpleasant odor.  Bad odors produced in this way are very harmful and likely to make us sick.  Many people have rotting potatoes and other vegetables in their cellars, and swill barrels, and heaps of refuse in their back yards.  These are all dangerous to health, and often give rise to very serious disease.  We should always remember that bad odors caused by decaying substances are signs of danger to health and life, and that these substances should be removed from us, or we should get away from them, as soon as possible.

3.  Germs.—­The chief reason why bad odors are dangerous is that they almost always have with them little living things called germs.  Germs are so small that they cannot be seen by the naked eye:  it takes a strong microscope to enable us to see them, but they are so powerful to do harm that if we receive them into our bodies they are likely to make us very sick, and they often cause death.

4.  Contagious Diseases.—­You have heard about diphtheria and scarlet fever and measles, and other “catching diseases.”  When a person is sick with one of these diseases, the air about him is poisoned with germs or something similar, which may give the same disease to other persons who inhale it.  So when a person is sick from one of these diseases, it is very important that he should be put in a room by himself and shut away from every one but the doctor and the nurse.  It is also necessary that all the clothing and bedding used by the sick person, and everything in the room, as well as the room itself, should be carefully cleansed and disinfected when the person has recovered, so as to wipe out every trace of the disease.  The writer has known many cases in which persons who have been sick with some of these diseases were careless and gave the disease to others who died of it, although they themselves recovered.  Do you not think it very wrong for a person to give to another through carelessness a disease which may cause his death?

5. Unhealthful vapors and odors of various sorts arise from cisterns and damp, close places under a house.  Rooms which are shaded and shut up so closely that fresh air and sunshine seldom get into them should be avoided as dangerous to health.