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. Very many kinds of bacteria and other germs are found nearly everywhere. They are in the soil and in water, and some float in the air as dust. When they fall on dead things, they cause _decay_ or _rotting_. When we can fruit, we kill the germs by boiling the fruit and the cans. Then we close the cans tightly so that no new germs can get into them. The fruit will then keep fresh for years. Decay is nearly always a good thing, for by it dead bodies and waste substances are destroyed and given back to the ground, where plants feed upon them. Many plants would not grow if they could not feed upon decaying things. So most bacteria and other germs are useful to us. But some kinds of germs will grow only in our bodies, and these kinds are the cause of most of our sickness. =199. Germs of sickness.=--We catch a sickness by taking a few of the germs of the sickness into our flesh. There they grow quickly, like weed seeds in the ground, and form crops of new germs within a few hours. After a few days the germs become millions in number, and crowd the cells of our flesh, just as weeds may crowd a potato plant (p. 54). Disease germs in the body also form poisons, just as some weeds in a field form poisons. The poisons make us sick, just as if we had swallowed the leaves of a poisonous weed. =200. Fever.=--If a sickness is caused by disease germs, the body is nearly always too warm. Then we say that the sick person has a _fever_. Almost the only cause for a fever is disease germs growing in the body. We can make a person have any kind of fever by planting a few of the germs of the fever in the right part of his body. We are made sick by the germs of fevers more often than by all other causes put together. Here is a list of common diseases caused by fever germs:--colds and sore throats, most stomach aches, blood poisoning in wounds, boils and pimples, tuberculosis, whooping cough, measles, chicken pox, diphtheria, scarlet fever, typhoid fever, smallpox, and malaria. Which of these kinds of sickness have you had? What sickness have you had besides these? =201. Sickness and Dirt.=--Disease germs leave the body of a sick person in three ways: first, through the skin, second, through the kidneys and intestines, and third, through the nose and throat. In these same ways our body gives off its waste matters. If we did not take anything from another person's body into our own body we should not catch fevers.