1 16 PA THOGENIC BACTERIA . 



whether bacteria by their growth produce acids or alka- 

 lies. 



The watery solution of litmus, being a vegetable in- 

 fusion, is likely to spoil, hence should always be treated 

 like the culture-media and sterilized by steam every time 

 the receptacle in which it is kept is opened. 



Peptone solution, or Dunham's solution, is very use- 

 ful for the detection of certain faint colors. It is a per- 

 fectly clear, colorless solution, made as follows : 



Sodium chlorid, 0.5 ^ Boil until the ingredients 



Whitte's dried peptone, i. > dissolve ; then filter, fill 

 Water, 100. J into tubes, and sterilize. 



It is the best medium for the detection of indol. In it 

 the Bacillus pyocyaneus produces its blue color. The 

 addition of 4 c.cm. of the following solution 



Rosalie acid, 0.5, 



80 per cent, alcohol, 100. 



makes it become an excellent reagent for the detection 

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

 If the bacterium produces acids, the color fades ; if alka- 

 lies, it intensifies. 



It is not intended that the student shall infer that 

 there are no culture-media other than these, which have 

 been selected because of their iisefulness and popularity. 

 Many other compounds and as many simple substances 

 are employed ; for example, eggs, white of egg, urine, 

 bread, sputum, sugar solutions, hydrocele fluid, and 

 aqueous humor. 



