80 SPIRILLUM CHOLERA 



the various spirilla from one another. Unfortunately 

 the discovery of many varieties of cholera spirilla and 

 of many allied organisms has tended to diminish the 

 value of this method of differentiation. The 

 characteristic growth of the spirilla of cholera in a 

 gelatine stab culture is shown in the two figures 

 (Fig. 79) and (Fig. 80) representing such growth at 

 21 C. after two and four days respectively. Growth 

 takes place along the whole length of the stab, but 

 much more rapidly near the surface, and at the 

 same time liquefaction of the gelatine takes place, 

 so that the whole assumes the appearance of a 

 funnel with a very long and narrow neck. The 

 fluid appears to shrink and the funnel to be occupied 

 by a refracting air-bubble floating on the upper part 

 of the culture. This appearance is probably due to 

 the clearing of the liquefied gelatine owing to the 

 sinking of the micro-organisms to the bottom of the 

 funnel. The collecting together and sinking of the 

 masses of organisms is seen in both figures, but with 

 greater clearness in the second ; in this the bottom 

 of the stab is filled with a plug of bacteria. The 

 rate of liquefaction of the gelatine and the cha- 

 racter of the resulting funnel of growth is very 

 variable with the different species of Spirillum 

 Cholerse. 



