SYNTHETIC MEDIA 



39 



Water, - 



Ammonium tartrate, 

 Potassium phosphate, 

 Magnesium sulphate, 

 Calcium chloride, - 



Prepare as above. 



Nsegeli's medium. 



Distilled water, 

 Glycerin, 

 Sodium chloride, 

 Calcium chloride, - 

 Magnesium sulphate, 

 Di-potassium phosphate, 

 Ammonium lactate, 

 Potassium aspartate, 



1000 grams. 

 10 



1 gram. 

 0-2 

 0-12 



Uschinsky's medium. 



1000 c.c. 

 30 grams. 

 5 



O'l gram. 

 0-2 



2 grams. 

 6 



3 rj 



The method of preparation is the same as in the other cases. This medium 

 was used by Uschinsky in his work on diphtheria toxin. 



SECTION II. SOLID MEDIA. 



The introduction of solid media into practical bacteriology is due to 

 Schroeter and especially to Koch. The commonest are transparent media, 

 prepared by adding to broth substances capable of making it solid at ordinary 

 temperatures ; but albumins coagulated by heat (serum, egg, etc.), meat 

 and certain vegetable media are also used. 



1. Gelatin media. 



Gelatin media are in very general use, and several different sorts are 

 prepared. 



General rules. 1. Use extra quality French gelatin, which is sold in thin 

 rectangular sheets weighing about 2*5 grams each. (Ordinary commercial 

 gelatin loses its property of solidifying if heated above 102-105 C. and 

 sterilization must therefore be effected at 100 C. ; this introduces an 

 unnecessary complication into the preparation of the medium.) 



2. Gelatin is very acid, and the medium must be neutralized after adding 

 it to the other constituents, but the addition of alkali must be stopped at the 

 neutral point or when the reaction is very slightly alkaline, because gelatin 

 will not solidify after being heated in alkaline solution. 



3. Ordinary" gelatin media liquefy at 25 C., and can therefore only be 

 used when the temperature of incubation is not to exceed 20-23 C. 



Ordinary gelatin. 



This medium is generally known simply as gelatin. 

 Method recommended. Proceed as in the preparation of broth. 

 1, 2 and 3. Macerate 500 grams of lean beef in a litre of water, heat, express 

 the fluid, filter while hot and make up the volume to a litre. 



4. To this broth add 



10 grams. 

 5 



a pinch (not essential). 

 80-150 grams. 



Peptone (Chapoteaut), 



Salt, 



Sodium phosphate, 



Extra quality gelatin, 

 The amount of gelatin required varies according to the time of year : in 

 winter 8 per cent. (80 grams per litre) is sufficient, but in summer as much as 

 10 to 15 per cent, is necessary say 120 grams per litre. 



