1 88 Culture Media and Bacteria Cultivation 



The medium is a very useful aid in differentiating the 

 typhoid and colon bacilli, showing well the alkali formation 

 of the former and acid of the latter. 



Peptone Solution, or Dunham's solution, is useful for the 

 detection of certain faint colors. It is a perfectly clear, 

 colorless solution, made as follows: 



Sodium chlorid 0.5 



Witte's dried peptone 1.0 



Water 100.0 



Boil until the ingredients dissolve ; filter, fill into tubes and sterilize. 



It was for a long time used for the detection of indol. A 

 very important fact in regard to peptone has been pointed 

 out by Garini,* who found that many of the peptones upon 

 the market were impure, and on this account failed to show 

 the indol reaction in cultures of bacteria known to produce 

 it. He recommends testing the peptone to be employed by 

 the use of the biuret reaction. The reagent used is Fehling's 

 copper solution, with which pure peptone strikes a violet 

 color not destroyed upon boiling, while impure peptone 

 gives a red or reddish-yellow precipitate. Both the peptone 

 and copper solution should be in a dilute form to make suc- 

 cessful tests. The addition of 4 c.c. of the following solu- 

 tion 



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 Smithf 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- 



* "Centralbl. f. Bakt. u. Parasitenk.," xm, p. 790. 



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



