48 General Bacteriology. 
EXERCISE XLII. COPMPARATIVE EFFICIENCY OF DRY AND MOIST HEAT. 
GENERAL DIRECTIONS. 
a. Charge a water blank with culture of a spore-bearing bacillus, shaking it well to 
break up the clumps. 
b. Sterilize eight cover-glasses by passing them several mee through the flame, and 
place four in each of two sterile Petri dishes. 
c. With a sterile loop place an equal quantity of the bacterial suspension (a.) on 
each cover-glass, and dry by placing Petri dishes in the incubator with the covers slightly 
raised. 
d. When dry place one Petri dish in the dry sterilizer (near the thermometer), and 
the other in the steamer. 
e. Keep both sterilizers at a temperature of 100° C., and at the end of 5, 10, 20 
and 40 minutes respectively, remove one cover-glass from each Petri, place it in a sterile 
Petri dish and pour a tube of liquefied gelatin or agar over it. Tip the dish from side 
to side to dislodge as many of the bacteria as possible from the cover-glass, solidify the 
medium and incubate. 
REFERENCES. L. 101; S. 146. 
SpeciaL Directions. Use an old (spore-bearing) culture of B. subtilis. Arrange 
data in the form of a table. 
EXERCISE XLII. EFFECT OF DESICCATION. 
GENERAL DIRECTIONS. 
a. Prepare five cover-glasses each of a spore-bearing and a non-spore-bearing cul- 
ture, as directed in XLII. 
b. Place them in a sterile Petri dish, and dry in the incubator. 
c. Next morning and every twenty-four hours later plate one of the cover-glasses. 
d. In this way determine the length of time the organism in question can withstand 
desiccation. 
REFERENCES. F.77; L. & N. 938; McF. 46; S. 151. 
Specisu DirEcTIoNS. Use a young culture of B. coli and an old (spore-bearing) cul- 
ture of B. subtilis. Tabulate results. 
EXERCISE XLIV. EFFECT OF CHEMICALS ON BACTERIA. 
GENERAL DIRECTIONS. 
a. Inoculate three tubes containing 10 ce. of sterile bouillon, with three loopfuls of 
a 24-hour old broth culture of organism to be studied. 
b. Add 0.1 ec. of a5% solution of carbolic acid to one tube (No. 1); 0.6 ee. to an- 
other (No. 2); and 2 cc. to the third (No. 3). 
c. Two hours later transfer three loopfuls from each tube to sterile bouillon and in- 
cubate all of the tubes at 38° C. 
d. The carbolic acid in No. 1 and its sub-culture does not prevent growth. In No. 
2 no growth, but abundant in its sub-culture (acts as an antiseptic). In both No. 3 and 
its sub-culture no growth (acts as a disinfectant) . 
REFERENCES. F. 81; L. & N. 90; L. 107; McF. 46. 
SPECIAL DirEcTIonS. Use B. coli. 
