192 



SPECIAL MEDIA 



Plaster =of=Paris Discs. 



i. Take large corks, 2 .5 cm. diameter, and roll a piece of stiff 

 note-paper round each, so that about a centimetre projects as a 

 ridge above the upper surface of the cork, and secure in position 

 with a pin (Fig. 112). 



2. Mix plaster-of -Paris into a stiff paste 

 with distilled water, and fill each of the cork 

 moulds with the paste. 



3. When the plaster has set, remove the 

 paper from the corks, and raise the plaster 

 discs. 



4. Place the plaster discs on a piece of 

 asbestos board and sterilise by exposing in the 

 hot-air oven to 150 C. for half an hour. 



Fig. 112. Cork 5. Remove the sterile discs from the oven 

 and paper mould for by means of sterile forceps, place each inside 

 plaster-of-Paris disc, a sterile capsule, and moisten with a little 

 sterile water. 



6. Sterilise in the steamer at 100 C. for thirty minutes on 

 each of three consecutive days. 



Gypsum Blocks (Engel and Hansen). 



These are in the form of truncated cones and for their prepara- 

 tion small tin moulds are required, each having a diameter of 5 . 5 

 cm. at the base and 4 cm. at the truncated apex. The height 

 (or depth) of a mould is 4 . 5 to 5 cm. 



1. Mix powdered calcined gypsum into a stiff paste with dis- 

 tilled water. 



2. Fill the paste into the moulds and allow it to set and dry by 

 exposure to air. 



3. Remove the block from the mould and transfer it to a 

 double glass dish of adequate size (7 cm. diameter X 7 cm. high). 



4. Sterilise block in its dish for one hour in the hot-air oven at 

 115 C. 



5. Carefully open the dish and add sterile distilled water to 

 moisten the block and form a layer in the bottom of the dish i cm. 

 deep. 



Wine Must. (Wine must is obtained from Sicily, in hermetically 

 sealed tins, in a highly concentrated form as a thick syrup 

 but not sterilised.) 



1. Weigh out "wine must," 200 grammes, place in a 2-litre 

 flask and add distilled water, 800 c.c. 



2. Weigh out ammonium tartrate, 5 grammes, and add to the 

 dilute must. 



3. Place the flask in a water-bath regulated to 60 C. for one 

 hour and incorporate the mixture thoroughly by frequent shaking. 



4. Filter through papier Chardin. 



5. Tube, and sterilise as for nutrient bouillon. 



