SPIRILLACE.E AND THE DISEASES CAUSED BY THEM 347 



in surface waters but certain waters, as for example the Ganges 

 River, destroy the cholera spirilla very quickly. This property- 

 has been ascribed to a weak acidity of the water. 



FIG. 138. Cholera vibrios, longer forms at higher magnification, showing long 

 flagella. (From Kolle and Schurmann after Zettnow.) 



Animals are not naturally susceptible to cholera. Koch gave 

 to a guinea-pig 5 c.c. of a 5 per cent solution of sodium carbonate 



FIG. 139. Involution forms of the spirillum of cholera. (Van Ermengen.) 



through a tube, and then 5 to 10 c.c. of water containing cholera 

 spirilla. The animal then received i c.c. of tincture of opium 



