PREPARATION OF CULTURE MEDIA 33 



1. Nutrient Broth. 



Meat infusion or meat extract 1000 c.c. 



Peptone 10 gm. 



Sodium chloride 5 gm. 



Warm the meat infusion to 50 C., add the peptone and salt and 

 stir until the peptone is dissolved. Add a little sodium hydrox- 

 ide to reduce the acidity, boil to coagulate the albumin present ; 

 ordinarily it is not necessary to clear with eggs. Add water to 

 make up for that lost by evaporation, adjust reaction, filter, and 

 tube or place in flasks for sterilization. Nutrient broth is of 

 service in obtaining the soluble toxins formed by bacteria and in 

 determining motility. 



2. Glucose Broth. 1 or 2 per cent glucose is added to nutrient 

 broth. The procedure is the same as in (1) except sterilization 

 should be by the fractional method. Glucose is a reducing agent, 

 consequently no free. oxygen can remain in a medium containing 

 it. Glucose broth on this account is used for the cultivation of 

 anaerobic organisms. 



3. Glycerin Broth. To broth (1) after filtration, 5 to 8 per 

 cent of glycerin is added. This medium is used especially for 

 growing the tubercle bacillus when tuberculin is to be prepared. 



4. Gelatin Medium. 



Meat infusion or extract 1000 c.c. 



Peptone 10 gm. 



Sodium chloride 5 gm. 



Gelatin (gold label) 100 gm. 



This is simply the above broth with the addition of gelatin as a 

 solidifying agent. The ingredients are dissolved by warming, 

 the reaction is adjusted, eggs are added to clear the medium 

 (page 19), and it is then heated for 15 minutes. Water is added 

 to make up the original volume; after being thoroughly stirred 

 the medium is filtered through cotton, tubed, and sterilized by 

 fractional sterilization. Characteristic growth takes place on 

 gelatin media which often facilitates identification. 



5. Agar Medium. 



Nutrient broth (1) 1000 c.c. 



Shredded agar 15 c.c. 



D 



