10 LABORATORY BACTERIOLOGY 
13. Labeling media and culture tubes. Stick on each tube 
of medium, about 3 cm. from the top, an adhesive white label 
about 2 cm. square. On the upper line should be written the 
name of the medium and the date of its preparation. Thus, 
“bouillon, 13-VII-1g00.””, When the tube is used the name of 
the organism or material with which it is inoculated, together 
with the date of inoculation, should be written on the lower 
lines. This applies to all media and tube or flask cultures. 
14. Titration of bouillon. Take 5 cc. of bouillon and place 
in a porcelain evaporating dish with about 45 cc. of water. Boil 
for three minutes. Add 1 cc. of a solution of phenol-phthalein. 
Stir and add to the solution in the evaporating disn enough 
of a N/zo NaOH solution from a burette to give it a clear, 
bright pink color. This amount then of N/zo NaOH solution 
is required to neutralize 5 cc. of the bouillon. A provisional 
standard reaction of + 1.5 to phenol-phthalein has been adopted. 
This would be slightly alkaline to litmus. In order to bring 
the entire amount of bouillon to the desired reaction (+ 1.5), 
subtract 1.5 from the amount of N/2o NaOH solution drawn 
from the burette and multiply the difference by the number 
of cc. of bouillon divided by 100. The product, if plus, repre- 
sents the amount of N/1 NaOH to be added; if minus, the 
amount of N/1 HCL to be added. After mixing, test the 
reaction again in the same way and add alkali or acid if needed. 
For greater accuracy further tests should be made. (For a 
more complete discussion of the reaction of culture media, see 
Appendix I.) 
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