THE PLATE PROCESS 55 



During these operations some plates should be under- 

 going sterilisation in the hot-air steriliser at a temperature 

 of 130 C. A box of sheet iron may be used with advantage 

 for this purpose, and is, moreover, capable of containing 

 a larger number of plates (fig. 24). After cooling, three 

 plates, which must only be seized by their corners, are next 

 taken out of the box and laid one after the other on Koch's 

 plate-making apparatus, on which they are cooled under a 

 bell-glass. In the absence of a hot-air steriliser the plates 

 may be sterilised in the interior of an oven, or in the gas 

 or spirit flame by holding them by the corners in the fingers 

 and heating both sides over the flame. 



Lid 



Case ~ 



Fu. 24. CASE QF SHEET-IRON FOR HOLDING THE PIATES. 



The plate apparatus (see p. 27) consists of a triangle with 

 feet formed by levelling screws, on which rests a glass vessel 

 covered with a thick plate of glass and filled before use with 

 iced water. It is rendered horizontal with the aid of a 

 spirit-level and covered with a bell-glass. The sterilised 

 plates having cooled under this bell, the first of the inocu- 

 lated test-tubes is then unplugged, its upper edge is heated 

 in order to sterilise that part over which the gelatine has to 

 flow, and its contents are poured from a small height upon 

 the plate in such a manner that the gelatine spreads out 

 over it in a fairly thin layer. In a short time the gelatine 

 sets under the bell-glass, and the plate is then brought into 

 a moist chamber and laid upon either little glass benches 



