Moisture and warmth make germs grow rapidly. A germ in growing lengthens out a little and then divides in the middle. It does this so quickly that one germ may become two in fifteen minutes. Each of these will then divide. In this way one germ can make many million germs in a single day ([Fig. 18]).
The Spoiling of Meat.—Fresh meat will not remain good even one day if left in a warm place. A large greenish blue fly seen buzzing about in warm weather will sometimes lay its eggs on meat. These will hatch the next day into little worms, called maggots. They grow rapidly and a few days later change into flies.
Fig. 18 —Drawing of the germ at the top every ten minutes, showing how it grew into two germs in a half hour. Much enlarged.
Germs will also spoil meat not kept cold. They feed on the meat and give off a poison, making it unfit to eat. The bad odor tells when the germs are at work. Every home should have a cold cellar or an ice box to keep food from spoiling.
Saving Food from Souring.—The souring of milk and of cooked food of any kind is due to the germs always present in the air and clinging by the thousands to unwashed dishes and hands. If meat or fruit is cooked and kept tightly covered, it will remain good for years. Many persons save fruit and vegetables for use in winter by putting them in jars, which are heated to kill the germs, and sealed tight to keep out other germs.
Fig. 19 —Yeast plants used in making bread and beer. Those on the right are growing new plants. Much enlarged.