Fig. 16 —Bacteria or microbes found in water, dust, and waste. They help change straw and other dead matter into food for plants. Much enlarged.
There are hundreds of different kinds of germs. Some are round like little balls and others are the shape of tiny rods. Many of them which look just alike act very different in growing. There are more than twenty different kinds that grow in our bodies and cause diphtheria, tuberculosis, and other diseases. We have measles and scarlet fever because we have gotten these disease germs from some one else in whom they were growing.
Fig. 17 —Mold which grew on moist bread in two days. 5, seed bodies breaking out of the sack; 1, 2, and 4, one of the seed bodies after one, two, and four hours' growth. Much enlarged.
Most germs feed on dead matter instead of our living bodies and make it melt away or change into another form. An apple or a piece of meat thrown out on the ground will soon change and become like the earth on which it lies. The change, called decay, is caused by millions of germs. The farmer's best friends are certain germs which help make the ground rich, so that the crops will grow.
Mold.—The dust raised in sweeping contains tiny living seedlike bodies. If these fall on bread, cheese, or fruit, and this food is afterward kept moist in a warm room for a day or two, they will grow into grayish fluffy spots. These spots are mold. The greenish white growth on the top of some canned fruit and on berries left in the warm kitchen over night is also mold.
Mold is a plant which grows from tiny round bodies acting like seeds ([Fig. 17]). These seed bodies of mold are common in all dust and often fly through the air. On this account food should be kept covered when possible and especially when one is sweeping. Some mold gives bread, cheese, and other food a bad taste, but it will not make one sick.
How Germs Grow.—Germs will not grow where it is very cold, but freezing the germs does not kill them. Boiling one minute kills most germs. Drying will stop the germs from growing, but will not kill all of them. Sunlight kills many of them.