Now, while there are many, many kinds of germs in the world, there are only certain ones that cause certain diseases, and we have learned where these germs like to live and how to kill them. We also know that they come only from some person or animal sick with the particular disease which they cause. Typhoid fever germs are not given off by a person suffering with tuberculosis, nor are diphtheria germs given off by a typhoid fever patient, but the germ of each disease is given off by some person or animal suffering from that particular disease. [Sidenote: How sickness due to germs can be prevented] If we kill all the germs that come from people sick with a certain disease, no one else can catch that disease. Knowing this, it seems unnecessary for anyone ever to be sick with disease that is caused by a germ. This is literally true, and the only reason that we have germ diseases is because we do not kill the germs that come from the sick people. Professor Irving Fisher of Yale University has said, "It is entirely possible to wipe out consumption within a single generation." It may not actually be done so quickly, but it is certain that the disease can finally be wiped out, though it may require many generations to accomplish it. Why, then, are germ diseases allowed to exist? Simply because so many people do not know the facts; and because many who do know will not take the trouble to kill the germs, even when they realize that some one else may get the disease as a result of their carelessness. What do you think of a woman who said, "I do not care if my neighbor's children do get scarlet fever from us; she is not a friend of mine, any way"? A woman has been heard to make such a statement to a health officer. It is just such people as this who spread disease. =Questions.= 1. How may germs be compared to seeds? 2. What do we know about disease germs that will help us to get rid of them? 3. How is it possible for us to get rid of consumption and other germ diseases? =Remember.= 1. While there are many kinds of germs in the world, only a few cause disease. 2. The germ that causes a certain disease will cause that disease and no other. 3. It is entirely possible to kill all the germs that cause disease. CHAPTER XVII ENCOURAGEMENT OF DISEASE BY UNCLEANLY HABITS We shall not try to learn here all the ways by which it is possible to destroy the germs of disease as they come from sick people. But there are certain rules (we sometimes call them fundamental principles) that you must know, if you hope to keep well and to prevent others from getting sick. [Illustration: FIG. 40. How diseases are frequently transmitted to children.] [Sidenote: Why we should stay away from the sickroom]