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XXVIII] tions two or more bacilli are united, in which case an S-shaped body is the result; or it may happen that several bacilli are thus united together, producing a spirillar appearance.

The comma bacillus is easily stained by watery solutions of fuchsin, or by Loffler's method, dried cover-glass films being used. It is decolorized by Gram. Dilute solution of methyl violet mixed with the intestinal contents and placed on a slide suffices for partial staining.

The bacillus grows best in alkaline media at a temperature of from 30° to 40° C. Growth is arrested below 15°, or above 42° C.; a temperature over 50° C. kills the bacillus. Meat broth, blood serum, nutrient gelatin, and potato are all suitable culture media. It multiplies rapidly without curdling in milk. It dies rapidly in distilled water; it survives longer if salt be added to the water.* For diagnostic purposes nutrient gelatin and potato are the most convenient culture media.

In gelatin plate cultivations minute white points appear; around these the gelatin liquefies, and the colonies of bacilli sink into funnel- or bubble-shaped depressions. By the end of the second or third day the culture is besprinkled with such depressions, liquefaction spreading peripherally until it involves the entire surface of the gelatin. The colonies are white or yellowish, very irregular in shape, granular, and shining like so many particles of ground glass. Later they assume a peculiar roseate hue, said to be absolutely characteristic.

In gelatin stab cultures the growth at first is most active near the surface; later, the colony sinking, liquefaction advances most below the surface of the gelatin, so that a bubble-shaped appearance is produced. Later still, as growth proceeds along the needle track, a finger-shaped liquefaction results, which in time extends to the sides of the tube. At the bottom of the liquefied area there is an accumu-