7. Every one ought to use his muscles some part of the day.
8. Alcohol and tobacco lessen the strength of the muscles.
CHAPTER XVI
DISEASE GERMS
197. Catching diseases.—Our body may get out of order like a machine. Some parts of it may be cut, or broken, or worn out, or hurt in other ways. Then we are sick until it is made whole again. Sickness always means that a part of the body is out of order.
Some kinds of sickness are like a fire. A small bit of something from a sick person may start a sickness in us, just as a spark may set a house on fire. Then we may give the sickness to others, just as a fire may spread to other houses. If a person has measles, we may catch the measles if we go near him; but if a person has a toothache, we cannot catch the toothache from him. So we may catch some kinds of diseases, but we cannot catch other kinds.
198. Bacteria and germs.—Every kind of catching sickness is caused by tiny living things growing in our flesh and blood. Some of them are tiny animals. Most of them are plants, and are called bacteria or microbes. A common name for all of them is germs.
The word germ means nearly the same as the word seed. Bacteria are so small that we cannot see them unless we look at them through a strong microscope. Then they look like little dots and lines (p. [54]). A million of them could lie on a pin point; but if they have a chance, they may grow in numbers, so that in two days they would fill a pint measure.