APPENDIX 349 



SPECIAL MEDIA 



Litmus lactose agar for demonstrating acid production 

 of microorganisms: Prepared the same as ordinary nutrient 

 agar (see Exercise 9, Part I), with the exception that 1% 

 lactose and 2% of the standard azolitmin solution is added 

 just after filtration, while the agar is still hot, and well 

 mixed through the agar before tubing. Sterilize by Tyndall 

 method. 



Dextrose calcium-carbonate agar for showing acid for- 

 mation by microorganisms: Prepared the same as ordinary 

 nutrient agar, with the exception that 1% dextrose and 1% 

 CaCOs are added to the hot agar just after filtration. The 

 added chemicals must be mixed well through the agar and 

 care must be taken during tubing that the CaCOs remains 

 in homogeneous suspension throughout the medium. Ster- 

 ilize by discontinuous method. 



Sour whey for determining the acid-destroying power 

 of microorganisms: Inoculate sweet milk with a pure active 

 culture of Bad. lactis acidi or Bact. bulgaricum as desired, 

 and place at about 30 C. Allow the maximum acidity to 

 form, cut the curd and heat in flowing steam for twenty 

 or thirty minutes. Strain through clean cheese-cloth and 

 allow to drain. Filter through filter paper. If clear whey 

 is desired, it will be necessary to clear the medium with 

 egg albumin. 



Butter fat for demonstrating fat decomposition: Melt 

 butter at about 100 C. and allow the casein to settle. 

 Decant the clear fat, place about 8 c.c. in sterile test tubes 

 and sterilize by the intermittent method. 



Other kinds of fat may be prepared similarly. 



Fermented agar for making solid synthetic media and 

 for testing food requirements and selective powers of bac- 

 teria: 1. Place a weighed amount (three parts) of agar in 

 a large bottle and to this add 200 parts of distilled water. 



2. Cover the mouth of the bottle with parchment paper 



