NUTRIENT MEDIA 49 



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-ounce 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 describe only the more 

 important ones now in use. Each investigator changes them 

 according to his taste. 



FLUID MEDIA 



Bouillon (According to Lb filer). A cooked infusion of 

 beef made slightly alkaline with sodium carbonate : 500 grams 

 of finely chopped raw lean beef is placed in a wide-mouthed 

 jar and covered with i liter 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 

 liter 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 albumin from coagulating, 10 parts of 

 peptone powder and 5 parts of common salt are added to every 

 1000 parts meat-water. For water analysis the salt must be 

 omitted. 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 

 4 



