SPIRILLUM CHOLERA ASIATICS. 171 



enlarges and extends along the track of the inoculating 

 needle, being broader at the surface and forming a short 

 funnel, which from the evaporation of the liquefied gelatin at 

 the top gives it a characteristic appearance (Fig. 68). 



Its growth on agar resembles very much the growth on 

 gelatin, but the medium is not liquefied. Milk is coagulated 

 by the formation of acids in the medium. In peptone- 

 bouillon the medium is clouded, and a pellicle forms on the 

 surface. 



Vitality. Its growth is very rapid, and advances best at a 

 temperature between 35 and 37 C., but continues at a tem- 

 perature as low as 17 C. Its growth is stopped at a tem- 

 perature of 16 C., and the bacterium is destroyed in five 

 minutes by an exposure to 65 C. Freezing does not destroy 

 it. Dryness destroys it very rapidly, but in the moist state 

 it may be kept frequently for several days and sometimes for 

 several months. 



Rapidity of Growth. When associated with other bacteria 

 in cultures it grows at first much more readily than any of 

 the known bacteria, having a tendency to form a surface 

 growth. At the end of eighteen to twenty hours, however, 

 it is outstripped in its growth by the other bacteria, and in 

 twenty-four to forty-eight hours its growth ceases altogether, 

 and in a few days scarcely any spirillum may be found in 

 the cultures. This is not due to the fact that it is destroyed 

 by its association with the other bacteria, but more because 

 the pabulum necessary for its growth is consumed. The 

 rapidity of the growth of this bacterium and the fact of 

 its growing on the surface of liquids are a great help in its 

 isolation from cholera dejecta, which when diluted with a 

 large amount of peptone-bouillon shows in a few hours a 

 peculiar surface growth, which consists almost of a pure 

 culture of cholera spirilla. 



Pathogenesis. None of the domestic animals contracts the 

 disease naturally. But their immunity seems to be due 

 to the fact that the bacteria that they ingest at the time 

 that they are exposed are destroyed by the acidity of the 

 gastric juice. 



