224 PRACTICAL BACTERIOLOGY. 



cause of cholera nostras, but it has since been dis- 

 covered to be only a harmless inhabitant of the 

 intestine, which multiplies with great rapidity during 

 intestinal catarrh. It can easily be distinguished 

 from the cholera bacillus by its growth upon gelatine, 

 which is much more energetically liquefied by the 

 former than by the latter. The colonies on gelatine 

 plates can be seen with a low power to have quite 

 clear sharp outlines, whilst no elevations or out- 

 growths are present ; further, on the third day, they 

 are twice as large as cholera colonies of the same age. 

 Still more striking are the differences shown in punc- 

 ture cultures in nutrient gelatine. No delicate whitish 

 thread is developed along the track of the needle, but 

 very soon a liquefaction funnel appears, which at first 

 is uniform in width throughout its length, but which, 

 during the course of development, becomes distinctly 

 thicker in the upper than in the lower layers of the 

 gelatine. Moreover, no bubble of air is ever formed 

 at the mouth of the liquefaction funnel, whilst even 

 by the third or fourth day the liquid gelatine has 

 spread to the sides of the test-tube. 



The cheese spirillum {Spirillum tyrogenum) comes 

 between the cholera bacillus and the Bacillus Finck- 

 leri, both as regards their morphology and their be- 

 haviour in cultivations. They have been found in old 

 cheese, and can be shown to be pathogenic in some 

 animals. They may be easily distinguished from the 



