174 CULTURE MEDIA 



Egg Medium (Dorset). 



1. Prepare 1000 c.c. of a 0.85 per cent, solution of 

 sodium chloride in a stout 2 -litre flask. 



2. Sterilise in the autoclave at 120 C for twenty 

 minutes. Cool to 20 C. 



3. Take 12 fresh eggs; wash the shells first with 

 water then with undiluted formalin: allow the shells 

 to dry. 



4. Break the eggs into a sterile graduated cylinder 

 and measure the total volume of the mixed whites 

 and yolks. Add one part sterile saline solution to three 

 parts mixed eggs. 



5. Transfer this mixture to a large wide-mouthed 

 stoppered bottle previously sterilised. Add sterile glass 

 beads and shake thoroughly in a mechanical shaker for 

 about thirty minutes, or whip with an egg- whisk. 



6. Filter through coarse butter muslin into a sterile 

 flask. 



NOTE. A few drops of alcoholic solution of basic fuchsin (suffi- 

 cient to give a definite pink colour) , or a few drops of waterproof 

 Chinese ink added to the medium at this stage facilitates the sub- 

 sequent "fishing" of colonies. 



7. Tube in quantities of 10 c.c. 



8. Solidify in the sloping position in the inspissator 

 at 75 C. for one hour. 



9. Place the tubes for forty-eight hours in the incu- 

 bator at 37 C., and eliminate any contaminated tubes. 



To prevent drying, 0.5 c.c. glycerine bouillon (see 

 page 209) may be added to each tube between steps 8 

 and 9. 



10. Cap those tubes of media which remain sterile 

 with india-rubber caps and store for future use. 



Potato. 



i. Choose fairly large potatoes, wash them well, and 

 scrub the peel with a stiff nail-brush. 



