THE GERM THEORY OF DISEASE (p. 86).--_What are Disease Germs?_-- Microscopical investigation has revealed throughout Nature, in the air, in water--especially when it contains organic matter, and even within the bodies of persons and animals, myriads of infinitesimal active organisms which live, multiply, and die in endless succession. These have been named _bacteria_ (bacterium, a rod, so called from the general rod shape first observed), and also _microbes_ (microbe, a small living object). Some investigators apply the latter term as a general one, limiting the former to such microbes as are believed to be special disease producers. The "Germ Theory" teaches that the seeds or _spores_ of bacteria, floating in the air we breathe or in the water we drink, are taken into our bodies where, under conditions favorable to their growth, they develop, multiply, and, each after its own species, produce distinctive evil results.--Thus, according to this theory, there are special varieties of microbes that cause, respectively, diphtheria, erysipelas, scarlatina, cholera, etc.--One of the most common microbes in nature is the bacterium of putrefaction, found everywhere in decaying organic matter. [Footnote: This is the microbe found in impure water. If we take half a glass of spring or river water, and leave it uncovered for a few days, we shall observe upon it a thin coating of what appears to be a fine dust. Place, now, a drop of this dusty water under a cover glass, and examine it under a microscope with a magnifying power of about five hundred diameters. The revelation is astonishing. "The whole field of the microscope is in motion; hundreds of bacteria, resembling minute transparent worms, are swimming in every direction with an undulatory motion like that of an eel or snake. Some are detached, others united in pairs, others in chains or chaplets or cylindrical rods....All these forms represent the different transformations of _Bacterium termo_, or the microbe of putrefaction. Those which are dead appear as small, rigid, and immovable rods."--TROUESSART.] By the species of microbes called ferments all fermented liquors are artificially produced (see p. 132); these also cause the "rising" of bread.--These wonderful little existences are thus made to perform an important part in the economy of Nature. "Nourished at the expense of putrefying organic matter, they reduce its complex constituents into soluble mineral substances, which they return to the soil to serve afresh for the nourishment of similar plants. Thus they clear the surface of the earth from dead bodies and fecal matter, and from all the useless substances which are the refuse of life; and thus they unite animals and plants in an endless chain."--TROUESSART.