So far as prevention is concerned, however, it makes practically little difference whether infectious diseases are due to an animal or a vegetable germ, or to one bacillus or another. They all have two things in common: they can be spread only by the touch of an infected person, and "touch" includes breath,--indeed "by touch" is the meaning of both infectious and contagious; and they can all be prevented by the strictest cleanness, or killed by various poisons known as germicides ("germ-killers"), or disinfectants. Most of these germicides are, unfortunately, poisonous to us as well; for, as you will remember, our bodies are made up of masses of tiny animal cells, not unlike the animal germs. Most of the germicides, therefore, have to be used against germs while they are outside of our bodies. Scripture says that "a man's foes shall be they of his own household," and this is true of disease germs. They grow and flourish--and, so far as history tells us, the diseases they cause seem to have started--only where people are crowded together in huts or houses, breathing one another's breaths and one another's perspiration, and drinking one another's waste substances in the well water. This fact has, however, its encouraging side; for, since this habit of crowding together, which we call civilization, or "citification," has caused and keeps causing these diseases, it can also cure them and prevent their spread if all the people will fight them in dead earnest. No amount of money, or of time, that a town or a county can spend in stamping out these infectious diseases would be wasted. Indeed, every penny of it would be a good investment; for, taken together, they cause at least half, and probably nearly two-thirds, of all deaths. Not only so, but most of the so-called chronic diseases of the heart, kidneys, lungs, bones, and brain are due to the after-effects of their toxins, or poisons. How Disease Germs Grow and Spread. But perhaps you will ask, "If these bacteria and protozoa are so tiny that we have to use a microscope, and one of the most powerful made, in order even to see them, how is it that they can overrun our whole body and produce such dangerous fevers and so many deaths?" The answer is simply, "Because there are so many millions of them; and because they breed, or multiply, at such a tremendously rapid rate." When one of these little bacilli breeds, it doesn't take time to form buds and flowers and seeds, like other plants, or even the trouble to lay eggs like an insect or a bird, but simply stretches itself out a little longer, pinches itself in two, and makes of each half a new bacillus.