lO 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-1900." 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 i cc. of a solution of phenol-phthalein. 

 Stir and add to the solution in the evaporating dish enough 

 of a N/20 NaOH solution from a burette to give it a clear, 

 bright pink color. This amount then of N/20 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/20 NaOH solution drawn 

 from the burette and multiply the difference by the nurnber 

 of cc. of bouillon divided by 100. The product, if plus, repre- 

 sents the amount of N/i NaOH to be added ; if minus, the 

 amount of N/i 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.) 



