126 



PATHOGENIC BACTERIA. 



to a faintly alkaline reaction. Definite varying degrees 

 of alkalinity can be secured by adding measured quan- 

 tities of the soda solution beyond that necessary to bring 

 about the beginning alkalinity. In using phenolphtha- 

 lein one should remember that the first sign of rose color 

 marks a change to alkalinity, and that this is a higher 

 degree of alkalinity than that required to turn red litmus 

 blue. 



The bouillon thus prepared is a clear fluid of a straw 

 color, much resembling normal urine in appearance. It 



21. Funnel for filling tubes with culture-media (Warren). 



is dispensed in previously sterilized tubes with cotton 

 plugsabout 10 c.cm. to each and is then sterilized by 

 steam three successive days for fifteen to twenty minutes 

 each, according to the directions already given for frac- 

 tional sterilization. (Seep. 109.) 



