17 
4. When cool, tubes 5a and 5b should be inoculated with a loopful of soil 
or tap water. (See Fig. 11.) 
5. Examine the tubes at each opportunity for two weeks. Tabulate the 
data as shown in Table I on the regular note paper. 
6. At the end of the observation period stain some of the milk and broth 
from tubes 4a and 4b, and 5a and 5b. Use carbol fuchsin, one minute for the 
broth, and methylene blue three minutes for the milk. 
TABLE I.—Sterilization of Milk and Broth 
Tube 
No. 
Treatment 
of 
beef broth 
Appearance 
after 
two days 
Appearance 
after 
one week 
Appearance 
after 
two weeks 
la 
2a 
3a 
4a 
5a 
Tube 
No. 
Treatment 
of 
milk 
Appearance 
after 
two days 
Appearance 
after 
one week 
Appearance 
after 
two weeks 
lb 
2b 
3b 
4b 
5b 
7. Describe efficient methods for the sterilization of milk and broth. 
(a) What was the macroscopic evidence that any milk or broth 
tubes were not sterile? Microscopic? 
(b) What does “sterile” mean? Which tubes were sterile? 
(c) Why is an autoclav temperature of 116° C more efficient than 
hot air oven temperature of 150° C? 
(d) Give a satisfactory method of sterilizing water, milk, Petri 
dishes, bandages, a room. 
