GELATIN MEDIA 41 



by raising the gelatin content to 15 per cent, the medium will remain solid at 

 summer temperature. 



An important point is to cool the tubes rapidly on taking them out of the auto- 

 clave, and to store them in a cold place as recommended by Abba. 



Fischer's gelatin. 



For the cultivation of phosphorescent bacteria Fischer recommends a 

 gelatin very rich in sodium chloride. To a litre of meat extract prepared 

 as above add 



Peptone (Chapoteaut), - 10 grams. 



Salt, - 30 



Gelatin (extra quality), - 80-120 



Dissolve, and proceed as in the preparation of ordinary gelatin. 



Liebig's gelatin. 



Dissolve 5 grams of Liebig's extract [Lemco] in 1000 grams of water (add 

 if necessary 10 grams of peptone, and 5 grams of salt), then add 100 grams 

 of gelatin, dissolve, and boil for 2 or 3 minutes. Neutralize and complete 

 the preparation as for ordinary gelatin. 



Buchner's gelatin. 



1. Dissolve with heat in a litre of water 



Gelatin (extra quality), - - 100 grams. 



Cane sugar, - - 20 

 Liebig's extract [Lemco], 5 ., 



Dry peptone, - 5 ,, 



2. To the solution add 



Tricalcium phosphate, - 5 grams. 



3. Boil for a few minutes, heat to 115 C., filter and proceed in the ordinary 

 way. 



Raisin gelatin. 



1. Make a decoction as described on p. 38, consisting of 250 grams of dried 

 raisins in a litre of water. 



2. Filter, then add 100 grams of gelatin and a pinch of sodium phosphate. Boil 

 for 2 or 3 minutes. Neutralize and finish as usual. 



Eisner's potato medium 



1. Take 500 grams of potatoes, peel and grate them. 



2. Macerate the pulp in a litre of water for 3 or 4 hours. 



3. Strain. Stand overnight. Decant the fluid. 



4. Make up the volume of fluid to a litre, and dissolve in it with gentle 

 heat 15 to 20 per cent. (150 to 200 grams) of gelatin. Boil for a few 

 minutes. 



5. The fluid is now very acid. Add normal soda solution until the 

 reaction is feebly but still distinctly acid. 



6. Heat to 115 C. for 5 minutes. Filter and complete the preparation 

 in the ordinary way. 



Choquet's gelatin. 



Choquet recommends the two following media for the cultivation of the 

 micro-organisms concerned in dental caries. 



1. Meat extract, 500 c.c. 



Gelatin (extra quality white), - - 35 grams. 



Peptone (Chapoteaut), - 5 



Calcium glycero-phosphate, - 5 ,, 



