430 BACTERIOLOGY. 



bacillus is not an easy matter. The cultural and morpho- 

 logical properties are subject to considerable variation. 

 Moreover, closely similar organisms may exist in river 

 water. These water vibrios phosphoresce, but this prop- 

 erty as in the case of other photogenic bacteria may disap- 

 pear on cultivation. It is doubtful whether the tr,ue cholera 

 vibrio can phosphoresce. 



The recognition of the cholera vibrio in water or in 

 suspected discharges is based upon the following charac- 

 teristics: 



« 

 1. — Microscopical appearance. 5. — Agar and gelatin tube cul- 

 :2. — Cultures in Dunham's solution. tures. 



3. — Appearance of colonies on 6.— Positive indol reaction. 



gelatin plates. 7. — Inoculation of guinea-pigs. 



4. — Appearance of colonies on 8.- — Pfeiffer's reaction. 



agar plates. 9. Agglutination. 



In the case of suspected intestinal contents, the micro- 

 scopical examination may in a few minutes justify a diag- 

 nosis of cholera, but a positive diagnosis can only be ob- 

 tained by confirming all the characteristics of the- organ- 

 ism. Under favorable conditions this may be accomplished 

 in less than 24 hours. A drop of the intestinal liquid should 

 be spread over the cover-glass, or better still, one of the 

 numerous flakes present in the rice-water discharge should 

 be thoroughly rubbed over the cover-glass. By staining 

 with carbolic fuchsin, the presence of comma-shaped or- 

 ganisms can be readily established if they are present in 

 large numbers. 



It should be remembered, however, that the cholera vib- 

 rio may disappear from the intestines after about the fifth 

 day. In other instances, only a few cholera vibrios may be 

 present and these may escape detection, owing to the large 

 number of other organisms that occur in the material. 



Even when only a few cholera germs are present in the 

 discharge or in the water, they can be brought to light by 

 -a peculiar method of ' ' accumulation. " Thus, when planted in 



