272 CLEAN MILK 



cohol are often required), dry residue, weigh and dissolve in water 



in proportions to make a 5% solution. Add 1/5 of 1% chloroform 



to the solution to preserve it. Of this solution, 10 to 15 c.c. per 



litre of media should give a good blue tint. Note : On autoclaving, 



most litmus media lose color entirely. The color returns on cooling 



and exposure to air. (Method of Minn. State Board of Health 



Laboratories). 



Cohn's Solution. 

 Distilled water, containing Per cent. 



Tribasic calcium phosphate 0.05 



Magnesium sulphate 0.50 



Acid potassium phosphate 0.50 



Ammonium tartrate 1 .00 



Sterilize by intermittent method in free steam. 



Uschinsky's Solution. 



Distilled water containing Per cent. 



Calcium chloride or 



Magnesium sulphate 02 



Acid potassium phosphate. 10 



Sodium chloride 50 



Ammonium lactate 1 .00 



Asparagin 34 



Glycerine 4.00 



Sterilize by intermittent method of free steam. 



Silicate Jelly. 



Solution (a) distilled water, containing — Per cent- 

 Calcium chloride 02 



Magnesium sulphate 10 



Ammonium sulphate 80 



Solution (b) distilled water, containing — 



Potassium phosphate *p 2 



Sodium carbonate 'W 1.2 



Solution (c) distilled water, containing 3.4$ si\j8c acid. 



Pour about 5-10 c.c. of (c) into a Petri dish : add, with stirring, a mixture of equal" 

 parts of (a) and (b). Sterilize intermittently in free steam ; streak upon the jelly thus- 

 prepared the organisms it is desired to grow. 



USES OF MEDIA. 



The chief media in ordinary use are valuable because each 

 elicits certain characteristics of bacteria which, taken together, per- 

 mit the recognition of the identity of the bacteria. The methods of 



