6 GLASS APPARATUS IN COMMON USE 



Filter Flasks or Kitasato's Serum Flasks (Fig. 7). 

 Various sizes, from 250 to. 2000 c.c. capacity. These 

 must be of stout glass, to resist the pressure to which 

 they are subjected, but at the same time must be 

 thoroughly well annealed, in order to withstand the 

 temperature necessary for sterilisation. 



All flasks should be either of Jena glass or the almost 

 equally well-known Resistance or R glass, the extra 

 initial expense being justified by the comparative 

 immunity of the glass from breakage. 



Petri's Dishes or "Plates" (Fig. 8, a). These have 

 now completely replaced the rectangular sheets of glass 

 introduced by Koch for the plate method of cultiva- 

 tion. Each "plate" consists of a pair of circular discs 

 of glass with sharply upturned edges, thus forming 

 shallow dishes, one of slightly greater diameter than 

 the other, and so, when inverted, forming a cover or 

 cap for the smaller. Plates having an outside diam- 

 eter of 10 cm. and a height of 1.5 cm. are the most 

 generally useful. A batch of eighteen such plates is 

 sterilised and stored in a cylindrical copper box (30 

 cm. high by 12 cm. diameter) provided with a " pull-off" 

 lid. Inside each box is a copper stirrup with a circular 

 bottom, upon which the plates rest, and by means of 

 which each can be raised in turn to the mouth of the box 

 (Fig. 9) for removal. 



Capsules (Fig. 8, b and c). These are Petri's dishes 

 of smaller diameter but greater depth than those termed 

 plates. Two sizes will be found especially useful 

 viz., 4 cm. diameter by 2 cm. high, capacity about 14 

 c.c. ; and 5 cm. diameter by 2 cm. high, capacity 

 about 25 c.c. These are stored in copper cylinders of 

 similar construction to those used for plates, but 

 measuring 20 by 6 cm. and 20 by 7 cm., respectively. 



Graduated Pipettes. Several varieties of these are 

 required, viz.: 



i. Pipettes of i c.c. capacity graduated in o.i c.c. 



