390 BACTEBIOLOOT. 



III. With another slimy flake start a culture iu a 

 tube of peptone solution — either the solution of Dun- 

 ham or, as Koch proposes, a solution of double the 

 strength of that of Dunham (Witte's peptone is to be 

 used, as it gives the best and most constant results). 

 Place this at 37° to 38° C, and at the end of from six 

 to eight hours prepare cover-slips from the upper layers 

 (without shaking) and examine them microscopically; 

 if comma bacilli were present in the original material, 

 and are capable of multiplication, they will be found in 

 this locality in almost pure culture. After doing this 

 prepare a second peptone culture from the upper layers 

 of the one just examined, 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 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, and at the 

 most, twenty-four hours after beginning the examina- 

 tion." (Koch.) 



There are certain doubtful cases in which the organ- 

 isms are present iu 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 



