[CHAPTER I]
CONSTANT DANGER OF ILLNESS
Every boy and girl confidently expects to grow into a strong and healthy man or woman. How often we hear a child say, "When I am a man," or "When I am a woman;" but I have never heard a boy or a girl say, "If I live to be a man or woman." When you think of what you will do when you are grown into men or women, it never occurs to you that you may be weak and sickly and therefore not able to do the very things that you would most like to do. This suggests that sickness is not natural, else the thought that you may perhaps become sick would enter your mind. As a matter of fact, most sickness is not natural.
The fight for life
There is a constant struggle going on in the world. You see a fight about you every day among the animals. You see the spider catch the fly, the snake catch the frog, the bird catch the insect, and the big fish catch the minnow; and you have heard of wars where men kill one another.
The greatest enemies that men have to fight, however, are not other men, or wild animals, but foes that kill more men, women and children every year than were ever killed in the same length of time by war. These foes are small, very small, but you must not think that because things are small they are not dangerous. We call these foes disease germs.
Fig. 1. Looking at cells
through a microscope.
Fig. 2. Some skin cells as seen
through a microscope.
The nature of a germ