TEXT-BOOK OF BACTERIOLOGY. 263 



obtain perfect preparations. The micro-organisms are decolored 

 by Gram's method. 



Upon the gelatin plate, after the usual time, small white dots 

 deep in the gelatin can be seen with the naked eye. These grad- 

 ually advance to the surface and then cause a rather slow liquefac- 

 tion of the gelatin. Funnel-shaped depressions are formed in the 

 transparent medium, increasing in depth rather than in circumfer- 

 ence, in the bottom of which the colony proper lies as a whitish 

 mass scarcely the size of a pin's head. The plate usually has on 

 the second or third day a quite peculiar appearance; it seems per- 

 forated with many small holes or air-bubbles. Liquefaction pro- 

 gresses only later; on the fifth or sixth day the third dilution, too, 

 usually has become completely diffluent. 



Under the microscope the colonies present an aspect peculiar 

 to the cholera bacteria. The smaller ones deep in the gelatin have 

 an irregular, receding, and occasionally rough or uneven margin ; 

 they are never circular, or at least sharply circumscribed, in the 

 beginning of development, like the colonies of most other bacteria. 

 They are of a bright white or pale yellow color, and in their texture 

 exhibit a remarkably uneven granulation. This will become more 

 manifest as they grow larger. The granulation becomes more and 

 more pronounced; the contents assume a peculiar lustre and glit- 

 ter; the color looks as if composed of little pieces of glass or crystal 

 grains. Incipient liquefaction is seen under the microscope by the 

 formation of a bright halo around the colony. A pale seam pro- 

 ceeds at a moderate distance from its margin corresponding to the 

 outer limit of the funnel-shaped depression, liquefying the gelatin 

 by the growth of the bacteria. At the same time we see in the 

 colony a roseate light, a reddish hue, to be found in no other kind 

 of bacterial growth. 



Development proceeds in the test-tube cultures as follows: A 

 growth occurs along the entire line of inoculation, but liquefaction 

 takes place more extensively only at the surface of the gelatin. A 

 funnel is formed similar to but very much larger than on the 

 plate; a deep depression is formed, appearing in the partly-softened 

 gelatin like an air-bubble, owing, presumably, to the very rapid 

 evaporation of the fluid produced. At this time the principal mass 

 of the culture accumulates close beneath the air-bubble, the central 

 portions of the inoculating puncture appearing as an almost empty, 

 shining thread in the gelatin, like a capillary tube blown out at the 

 end; the bacteria which had been developing have descended into 

 the lower third of the puncture, where they settle as yellowish- 

 white masses loosely curled. 



