68 



SOLID CULTIVATION MEDIA. 



Their sterility is now attained ; but to obviate any risk of its being 

 incomplete, it is well to keep them under observation for a week be- 

 fore using them ; when, if no reaction has occurred, they may safely 

 be employed as sterile soil. 



Inoculation of Bread Paste. 



42. The platinum wire already described is used for the in- 

 oculation. A flask containing sterile bread paste is inverted, and 

 held thus in the left hand (see Fig. 27). Its cotton wool plug is 

 then twisted round, to break down any adhesions between it and 



Fig. 27. — Inoculation of bread paste. 



the neck of the flask, and is then withdrawn, and held between two 

 fingers of the same hand, with its lower end pointing towards the 

 ground. This arrangement is to avoid risks from the gravitation of 

 germs through the atmosphere. The platinum wire is now sterilised, 

 charged with seed material, and its tip repeatedly plunged into the 

 mass of paste at the bottom of the sterile flask. It is then withdrawn, 



