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Exercise 38. Test of Disinfectants 
MATERIALS: 
A 10 per cent solution of carbolic acid 
A 1:500 solution of mercuric chloride 
8 tubes of plain broth reaction pH 7.0. 
1 tube of sterile distilled water 
2 empty sterile test tubes 
1 box of sterile 1 cc. pipettes 
Burettes for measuring disinfectants 
Culture of Escherichia coli 
Culture of Bacillus anthracis 
Much misinformation is prevalent concerning the value of disinfectants. In 
order to gain some first-hand knowledge concerning some of the disinfectants 
in common use, two will be examined. 
Each student will test one disinfectant. The disinfectants will be assigned 
by the instructor. 
Escherichia coli will be used for example of a non-spore-forming organism 
and Bacillus anthracis will be used as an example of a sporogenous type. 
1. Make an agar streak culture of Escherichia coli and of Bacillus anthracis. 
Place the cultures in the 30° C. incubator for 48 hours. 
2. By means of a sterile 1 cc. pipette measure 4 cc. of sterile distilled water 
into each of the two sterile test tubes. Label one tube Escherichia coli and the 
other B. anthracis. 
3. By means of the sterile loop prepare suspensions of the two cultures, 
transferring organisms from the agar streak cultures. 
4. Using care to avoid contamination measure with a burette, 4 cc. of the 
disinfectant assigned, into each of the suspensions of bacteria. The dilution 
produced will allow a 5 per cent solution of phenol or a 1:1000 solution of 
mercuric chloride to act upon the bacteria. 
TABLE XIV.—Exposure Table for Disinfectant Tests 
Escherichia coli 
Bacillus Anthracis 
3 minutes 
lM hours 
10 minutes 
24 hours 
30 minutes 
48 hours 
1 Y* hours 
72 hours 
