PATHOGENIC BACTERIA. 323 



animals has been recommended as an additional means of 

 diagnosis between the cholera spirillum and related forms. 

 The agglutinating power which the blood of animals im- 

 munized to cholera has for the cholera spirillum may be 

 employed in the same way. 



In the examination of water for the spirillum of cholera, 

 to i liter, or more, of water, add enough of a strong pep- 

 tone solution to make it contain i per cent, peptone and 

 .5 per cent, sodium chloride. (The strong peptone solution 

 contains 20 per cent, peptone and 10 per cent, sodium 

 chloride; is alkaline and sterile.) The water, with the 

 peptone in it, is divided among a number of sterilized 

 flasks. After twelve hours in the incubator, any vibrios in 

 it are likely to have multiplied and to have formed a scum 

 on the surface, which may be investigated for the char- 

 acteristics of the spirillum of cholera according to the 

 methods given above. See also page 142. 



Since Koch's discovery of the cholera spirillum in 

 1883-84 a considerable number of bacteria have been 

 described which resemble the cholera spirillum more or 

 less closely, and which have to be taken into account in 

 making examinations of material of any sort for it. This 

 is particularly necessary in the investigation of water, in 

 which such spirilla seem to occur quite frequently. 



Vibrio Metchnikovi. A comma-shaped organism, 

 which though somewhat shorter and thicker may be very 

 similar to the comma bacillus of cholera in form, and which, 

 like it, may sometimes form genuine spirilla. It is motile 

 and has a flagellum at one end. It does not form spores. 

 It is aerobic. It stains with the aniline dyes, and is not 

 stained by Gram's method. It grows at the room tempera- 

 ture. It liquefies gelatin somewhat more rapidly than the 

 spirillum of cholera. The colonies on gelatin plates are 

 not all alike; some of them resemble those of vibrio pro- 

 tens, and others are extremely like those of the spirillum of 

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