22 ELEMENTARY BACTERIOLOGY LABORATORY EXERCISES 
Formula 
500 grams lean ground beef per liter 
1.0% peptone 
Distilled water 
Reaction, pH 7.0 
Procedure 
(1) Add 500 grams of ground lean beef to 1000 c.c. of distilled water and 
mix thoroughly. 
(2) Hold in a refrigerator at about 10° C. for 24 hours. 
(3) Remove the meat from the bouillon by straining through cheesecloth. 
(4) If necessary, remove the excess fat. 
(5) Add one per cent of peptone and dissolve. 
(6) Adjust the reaction. 
(7) Heat in the autoclave for 15 minutes under 15 pounds pressure. 
(8) Filter through paper and make the solution up to 1000 c.c. by adding 
distilled water. 
(9) Sterilize in the autoclave for 30 minutes at 15. pounds pressure. 
A solid medium can of course be prepared by the addition of agar or gelatin 
to this broth. 
EXERCISE 36 
CARBOHYDRATE MEDIA 
The addition of carbohydrates and related compounds (simple sugars, poly- 
‘ saccharids, polyhydric alcohols, and glucosides) to culture media is a common 
practice in bacteriological work. Usually such media are simply the standard 
nutrient media described in Exercises 32 to 35 with one per cent of the particular 
carbohydrate added. 
In the preparation of carbohydrate media, especially in the cases of simple 
sugars, the carbohydrate should be added to the rest of the ingredients just prior 
to filtration and sterilization in order to obviate unnecessary heating, as there is 
some danger of slight hydrolysis of the sugar at high temperatures, especially in 
the presence of the other constituents of the medium. For this reason, in cases in 
which particular accuracy is desired, solutions of the sugars are sometimes steril- 
ized separately and then added to the medium just before use. 
It is also a common practice to use indicators in carbohydrate media to de- 
tect the presence of specific organisms which have the power of fermenting the 
carbohydrate in question; for example, the use of lactose agar with the addition 
of an indicator, such as litmus or brom cresol purple, for the detection and isola- 
tion of lactose fermenting bacteria in water or milk. 
