DIAGNOSIS OF ASIATIC CHOLERA. 337 



pure culture. After doing this prepare a second 

 peptone culture from the upper layers, also a set of 

 gelatin plates, and with what remains make the test 

 for indol by the addition of ten drops of concentrated 

 sulphuric acid for each ten cubic centimetres of fluid 

 contained in the tube. If comma bacilli are growing 

 in the tube the rose color characteristic of the presence 

 of indol should appear. 



By following this plan "a bacteriologist who is 

 familiar with the morphological and biological pecu- 

 liarities of this organism should make a more than 

 probable diagnosis at once by microscopic examination 

 alone, and a positive diagnosis in from twenty to, at the 

 most, twenty-four hours after beginning the examina- 

 tion." (Koch.) 



There are certain doubtful cases in which the organ- 

 isms are present in the intestinal canal in very small 

 numbers, and microscopic examination is not, therefore, 

 of so much assistance. In these cases plates of agar- 

 agar, of gelatin, and cultures in the peptone solution 

 should be made. 



The plates of agar-agar should not be prepared in 

 the usual way, but the agar-agar should be poured 

 into Petri dishes and allowed to solidify, after 

 which one of the slimy particles may be smeared 

 over its surface. The comma bacillus, being mark- 

 edly aerobic, develops very much more readily when 

 its colonies are located upon the surface than when 

 they are in the depths of the medium. A point 

 to which Koch calls attention, in connection with this 

 step in the manipulation, is the necessity for having the 

 surface of the agar-agar free from the water that is 

 squeezed from it when it solidifies, as the presence of 



