[Gk. baktron, a rod or stick.] The name of a family of extremely minute plants, consisting of a single cell, and only visible under a high power of the microscope. They are found almost everywhere, and all fermentation and putrefaction are due to them. While the most of them are harmless, and very useful in removing decaying substances, others are highly dangerous to life, forming the "germs" or "microbes" of contagious diseases. This fact was first discovered by Louis Pasteur, and gave rise to the science of Bacteriology. The harmful bacteria enter the body of animals, multiply with extreme rapidity, and give off poisonous products or toxins which cause violent and often deadly diseases. Among these are yellow fever, cholera, smallpox, diphtheria, malarial and typhoid fevers, and various others, also anthrax and other diseases of the lower animals. In the treatment, the use of anti-toxins, prepared by inoculating animals with weakened bacteria, has proved of much service, but the science of bacteriology is so recent that much remains to be learned.