470 BACTERIOLOGY. 



ity in almost pure culture. After the microscopic exami- 

 nation prepare a second peptone culture from the upper 

 layers of the one just examined, also a set of gelatin 

 plates, and with M^hat remains make the test for indol 

 by the addition of 10 drops of concentrated sulphuric 

 acid for each 10 c.c. 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 peculi- 

 arities of this organism should make a more than prob- 

 able diagnosis at once by microscopic examination alone, 

 and a positive diagnosis in from twenty to, at most, 

 twenty-four hours after beginning the examination." 

 (Koch.) 



In certain doubtful cases the organisms are present in 

 the intestinal canal in very small numbers, and micro- 

 scopic examination is not, therefore, of so much assist- 

 ance. 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 markedly aerobic, develops 

 very much more readily when its colonies are located 

 upon the surface then when in the depths of the med- 

 ium. A point to which Koch calls attention, in con- 

 nection with this step in manipulation, is the necessity 

 of having the surface of the agar-agar free from 

 the water squeezed from it when it solidifies, as the 

 presence of the water interferes with the development 

 of the colonies at isolated points and causes them to 



