208 Culture Media and Bacteria Cultivation 



successful tests. The addition of 4 c.c. of the following 

 solution 



Rosolic acid 0.5 



Eighty per cent, alcohol 100.0 



makes the peptone solution a reagent for the detection of 

 acids and alkalies. The solution is of a pale rose color. 

 If the organisms cultivated produce acids, the color fades; 

 if alkalies, it intensifies. As the color of rosolic acid is de- 

 stroyed by glucose, it cannot be used in culture media con- 

 taining it. 



Theobald Smith* has called attention to the fact that 

 many bacteria fail to grow in Dunham's solution, and 

 recommends that, for the detection of indol, bouillon free of 

 dextrose be used instead. All bacteria grow well in it, and 

 the indol reaction is pronounced in sixteen-hour-old cultures. 

 His method of preparation is as follows : Beef -infusion, pre- 

 pared either by extracting in the cold or at 60 C., is inocu- 

 lated in the evening with a rich fluid culture of some acid- 

 producing bacterium (Bacillus coli) and placed in the ther- 

 mostat. Early next morning the infusion, covered with a 

 thin layer of froth, is boiled, filtered, peptone and salt added, 

 and the neutralization and sterilization carried on as usual. 



This method is subject to error caused by the presence in 

 the medium of indol produced by the colon bacillus. This 

 can be demonstrated if the tests for indol be sensitive. 



Other culture media employed for special purposes will be 

 mentioned as occasion arises. 



* "Journal of Exp. Medicine," Sept. 5, 1897, vi, p. 546. 



