_Bacteria_ and _Torulæ_ being already in existence, they may, undoubtedly, reproduce organisms similar to themselves by processes of fission and gemmation--in the same way that other low protistic organisms propagate their kind. Although so many reasons rendered this view probable, it was some time before I was able actually to confirm it by personal observations in the case of _Bacteria_. In the ordinary microscopical examination of portions of an infusion containing these organisms, an observer may watch for hours and never see a single instance of such fission occurring. His attention is apt to be distracted by the number of organisms which are constantly flitting before his view, and he is, moreover, perhaps apt to pay particular attention to those which seem by their movements to be most obviously alive. I have observed the process most plainly when a few _Bacteria_ have been enclosed in a single drop of fluid, pressed into a very thin stratum, in a “live-box” kept at a temperature of about 90° Fahr. by resting on one of Stricker’s warm-water chambers placed on the stage of the microscope. Under these conditions, I have seen a _Bacterium_ of moderate size divide into two, and each of these into two others somewhat smaller, in the course of fifteen minutes. It is still more worthy of remark, that in all cases (so far as I have been able to observe), this, the most certain sign of vitality which such organisms are capable of manifesting, is shown by those which, from their stillness, might be considered dead. The _Bacteria_ which are about to divide are generally either motionless,[1] or merely present slight oscillating movements. The separation is quickly brought about at the joint, so that the original organism divides into two equal portions; and these, lying close together, soon develop a new construction as they grow, through which a further division may occur. [1] Those which are quite motionless are always in close apposition either with the under surface of the covering glass, or with the surface of the glass on which they are situated.