204 SPECIAL MEDIA 



and add distilled water in the proportion of i c.c. for every 

 gramme weight of potato. Allow the flask to stand in the ice- 

 chest for twelve hours. 



3 . Strain the mixture through butter muslin and filter through 

 Swedish filter paper into a graduated cylinder. Note the amount 

 of the filtrate. 



4. Place the filtrate in a flask, add an equal quantity of dis- 

 tilled water, and heat in the steam steriliser for sixty minutes. 



5. Add glycerine, 4 per cent., mix thoroughly, and again 

 filter. 



6. Tube and sterilise as for nutrient bouillon. 



Potato Gelatine (Eisner). 



1. Take i kilo of potatoes, wash thoroughly in water, peel, 

 and finally grate finely on a bread-grater. 



2. Weigh the potato gratings, place them in a 2 -litre flask, 

 and add distilled water in the proportion of i c.c. for every gramme 

 weight of potato. Allow the flask to stand in the ice-chest for 

 twelve hours. 



3. Strain the mixture through butter muslin, and filter through 

 Swedish filter paper into a graduated cylinder. 



4. Add 15 per cent, gelatine to the potato decoction and 

 bubble live steam through the mixture for ten minutes. 



5. Estimate the reaction; adjust the reaction of the medium 

 mass to + 25. 



6. Cool the medium to below 60 C. ; clarify with egg as for 

 nutrient gelatine (vide page 166). 



7. Add i per cent, potassium iodide (powdered) to the medium. 



8. Filter through papier Chardin. 



9. Tube and sterilise as for nutrient gelatine. 



Aesculin Agar. (B. coli and allied organisms give black 

 colonies surrounded by black halo.) 



1. Measure out 400 c.c. distilled water into a tared 2-litre flask. 



2. Weigh out 



Agar 15 grammes 



Peptone 10 grammes 



Sodium taurocholate 5 grammes 



and make into a thick paste with 150 c.c. distilled water. 



3. Add this paste to the distilled water in the flask. 



4. Dissolve the ingredients by bubbling live steam through the 

 mixture. 



5. Weigh out 



Aesculin i . o gramme 



Ferric citrate 0.5 gramme 



and dissolve in a second flask containing 100 c.c. distilled water. 



6. Mix the contents of the two flasks adjust the weight to 



