ELEMENTARY BACTERIOLOGY LABORATORY EXERCISES 11 
SECTION 4: THE CULTURE OF BACTERIA 
EXERCISE 15 
BROTH CULTURES 
Treat three tubes of nutrient broth, or bouillon, as follows: 
(1) Label one tube “Control” and leave uninoculated. Do not remove the 
cotton plug. 
(2) Remove the cotton plug from one tube and add a small amount of dirt 
or other foreign material. Replace the cotton plug. 
(3) With the wire loop inoculate the third tube of broth from the pure 
culture furnished, 
Observe carefully the technique used and the precautions taken in making 
transfers. 
Incubate at 37° C. The inoculating needle should always be heated to red- 
ness, and the lower end of the handle passed through the flame several times, 
immediately before and after making a transfer. Also, the mouths of the tubes 
from which cultures are taken and into which they are transferred should be 
passed through the Bunsen flame immediately before and after the needle is in- 
troduced and removed. After incubation for two days, make observations. 
EXERCISE 16 
AGAR SLOPE CULTURES 
Melt two tubes of nutrient agar in boiling water. When melted, cool to a tem- 
perature of 42° to 45° C. Remove from water and allow to harden in a slanting 
position. 
When cold and solid, make a streak culture, as demonstrated, from the pure 
culture furnished. Keep the other tube sterile as a control. Incubate‘at 37° C. 
In inoculating slope cultures the needle should be drawn gently over the 
surface of the agar from the butt to the top of the sloped surface. Care should be 
taken not to scratch the agar surface. The same technique and precautions as ex- 
plained in Exercise 15 should always be observed in the handling of cultures. 
Observe after incubation for two days. 
