Size.
—Bacteria vary greatly in size. Average rod-shaped bacteria are about 1/25000 of an inch long, but there are undoubtedly organisms so small that they cannot be seen, even by means of the strongest microscopes we now possess.
Staphylococci. Streptococci. Diplococci. Tetrads. Sarcinæ.
Fig. 2.—(Williams.)
Motion.
—The power of motion in certain species of bacteria is due to hair-like appendages called flagella. These flagella by a lashing movement somewhat resembling the action of oars enable the organisms to move through fluids.
Multiplication.
—After bacteria have fully developed, each cell divides into two equal parts; the process of division is called fission. Each
of these two parts rapidly grows into a full-sized organism. Then fission again takes place, so that four bacteria replace the original one. In each of the four, fission occurs again, and so the process of multiplication continues. As bacteria develop they group themselves in characteristic ways. Some, like the streptococci, arrange themselves in chains; the diplococci, in pairs; the tetrads, in groups of four; others in packets called sarcinæ, and still others, the staphylococci, form masses supposed to resemble bunches of grapes.
