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Bacteria. (Gr. bakterion, a rod). A class of very minute microscopic organisms, often of a rod-like form, which are regarded as of vegetable nature, and as being the cause of putrefaction; they are also called microbes or microphytes. The genus Bacterium, in a restricted sense, comprises microscopic unicellular vegetable organisms without chlorophyll which multiply by transverse division of the cells. Species are found in all decomposing animal and vegetable liquids. Bacteria are of various shapes. The bacillus forms rods which divide into two; these increase in length and divide again. Micrococcus consists of single rounded cells. Streptococcus forms chains of rounded cells. Sarcinae form irregular cubes. Spirillum is spiral in form. While many forms of bacteria are harmless or even beneficial to man, others are known to be the cause of diseases which are contagious or infectious, such as scarlet fever, typhoid fever, tuberculosis, and many others.

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