272 PATHOGENIC BACTERIA. 



in size, and attain a peculiar transparent character which 

 is suggestive of powdered glass. The commencement 

 of liquefaction causes the colony to be surrounded with a 

 transparent halo. When this occurs the colony begins to 

 sink, from the digestion and evaporation of the medium, 

 and also to take on a peculiar rosy color. 



In puncture-cultures in gelatin the growth is again so 

 characteristic that it is quite diagnostic (Fig. 80). The 



FIG. 80. Spirillum cholera Asiatica ; gelatin puncture-cultures aged forty- 

 eight and sixty hours (Shakespeare). 



growth takes place along the entire puncture, but devel- 

 ops best at the surface, where it is in contact with the 

 atmosphere. An almost immediate liquefaction of the 

 medium begins, and, keeping pace with the rapidity of 

 the growth, is more marked at the surface than lower 

 down. The result of this is the occurrence of a short, 

 rather wide funnel at the top of the puncture. As the 

 growth continues evaporation of the medium takes place 

 slowly, so that the liquefied gelatin is lower than the 

 solid surrounding portions, and appears to be surmounted 

 by an air-bubble. 



