The family of _Vibrionidæ_, so named from their darting or quivering motion, includes the eel-like microscopic animalcules which occur in stale paste, vinegar, &c., with some others, which are parasitic on living vegetables, such as _Vibrio tritici_, which infest the grains of wheat, producing the destructive disease called corn-cockle or purples. They are filiform animals, extremely slender, without appreciable organization, internal stomach, or apparent organs of locomotion. They are the first animalcules which show themselves in any infusion of organic matter. By using microscopes of the highest magnifying power, traces of very thin, short lines can be perceived, either straight or sinuous, the thickest of them not exceeding the thousandth part of the fraction of an inch. They are contractile, and propagated by spontaneous division, or _fission_. Among them some resemble right lines, more or less distinctly articulated, and endowed with a very slow movement; these are _Bacteridæ_. Others are flexuous and undulating, and more or less lively; these are true _Vibrions_. Others have the body fashioned in the form of a corkscrew, turning unceasingly upon themselves with great rapidity; these are the _Spirillidæ_, having an oblong fusiform or filiform body, which undulates or turns spirally upon itself. [Illustration: Fig. 30. Bacterium, termo (Müller), magnified 600 times. The same, magnified 1600 times.] The _Bacterium termo_ (Fig. 30) is the smallest of the Infusoria. It is found, at the end of a short time, in all vegetable or animal infusions exposed to the air. It shows itself in infinite numbers, forming swarms of animalcules, which disappear as other species multiply in the liquid, to which animals it serves for nourishment. When the infusion becomes too foetid for these new species to live in it, in consequence of fermentation or putrefaction, the _Bacterium termo_ reappears. This species was one of the first observed; Leuwenhoek found it in the white matter in the teeth and gums, which is called teeth tartar. It is also found in the fluids of various animals which have been affected by disease. [Illustration: Fig. 31. Vibrion baguette (Müller), magnified 300 times.]