36 PA THOGENIC BA CTERIA. of these is much less clear. It seems to be an effort to convert the entire microbe into a permanent form. This process is observed particularly in the micrococci, where the substance of a cell is said to break up into segments, each of which becomes a resisting body fruitful in prop- agating its species. Of the arthrospores little has, so far, been learned. It is not improbable that among the micrococci, and also among some of the smaller bacilli in whom no spores have been observed, the maintenance of the species when conditions of life become unfavor- able is due to the assumption of a permanent form by some of the individuals, without the formation of any spore-like bodies. This is at present largely a matter of conjecture, but the indications pointing in that direction are numerous. It is believed by Frankel and others that sporulation in the bacteria is not a sign of the exhaustion of nutri- tion, but a sign of the vital perfection of the organism. These observers regard spore-formation as analogous to the flowering of higher plants, which takes place only when the conditions and development are best. Morphology.—The morphology of the bacteria is quite varied. Three principal forms, however, exist, from which the others seem to be but variations. The most simple appear as minute spheres, and from yL ^.^ la /^»/Tk. @®@O® ^ _ FIG. 2.—Diagram illustrating the morphology of the cocci: a, coccus or micrococcus; £, diplococcns;