48 ESSENTIALS OF BACTERIOLOGY. 



brush, placed obliquely to drain, and when dry corked with 

 cotton plugs. Then put in the hot-air oven (little wire-cages 

 being used to contain them) for fifteen minutes, after which they 

 are ready to be filled with the nutrient media. (The cotton 

 should fit firmly in the tube and extend a short space beyond it.) 



Test-tubes without flaring edges are more desirable since the 

 edges can easily be drawn out so as to seal the tube. 



Instead of test-tubes, ordinary 3 oz. panel medicine bottles 

 can be used for retaining the nutrient media and cultures. 



According to late investigations, the glass tubes become suffi- 

 ciently sterile in the steam-chest without the preliminary sterili- 

 zation in the dry oven. 



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 Loftier). A cooked infusion of beef 

 made slightly alkaline with soda carbonate : 500 grammes of 

 finely-chopped raw lean beef are placed in a wido-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, the white meat remaining 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 



