46 ESSENTIALS OF BACTERIOLOGY. 



CHAPTER VIII. 



NUTRIENT MEDIA. 



OF the many different media recommended and used since 

 bacteriology became a science, we can only describe the more 

 important ones now in use. Each investigator changes them 

 according to his taste. 



FLUID MEDIA. 



Bouillon (according to Loffler). A cooked infusion of chopped 

 beef made slightly alkaline with carbonate of soda. Prepared 

 as follows : 500 grammes of finely-chopped raw lean beef are 

 placed in a wide-mouthed jar and covered with 1 litre of water ; 

 this is left standing twelve hours with occasional shaking. It is 

 then strained through cheese cloth or straining cloth, the white 

 meat remaining in the cloth being pressed until one litre of the 

 blood red meat- water has been obtained. The meat-water must 

 now be cooked, but before doing this, in order to prevent all the 

 albumen from coagulating, 10 parts of peptone powder and 5 

 parts of common salt are added to every 1000 parts meat-water. 

 It is next placed in the steam-chest or water-bath for three- 

 quarters of an hour. 



Neutralization. The majority of bacteria grow best on a 

 neutral or slightly alkaline soil, and the bouillon, as well as 

 other media, must be carefully neutralized with a sat. sol. of 

 carbonate of soda. Since too much alkalinity is nearly as bad 

 as none at all. the soda must be added drop by drop until red 

 litmus paper commences to turn blue. The bouillon is then 

 cooked another hour, and filtered when cold. The liquid thus 

 obtained must be clearly alkaline, and not clouded by further 

 cooking. If cloudiness occur, the white of an egg and further 

 boiling will clear the same. 



Sterilization of the bouillon. Erlenmeyer flasks (little conical 

 glass bottles) or test-tubes plugged and properly sterilized are 

 filled one-third full with the bouillon, and placed with their con- 

 tents in the steam-chest. A tin pail with perforated bottom 



