28 BACTERIOLOGY 



and agar can be filtered while warm through a suitable 

 glass funnel inserted into the hot-water filter (fig. 15). 



Apparatus for plate-cultivations, For the purpose of 

 spreading nutrient gelatine upon plates a levelling apparatus 

 is in use which must be so arranged that the plate lies 

 horizontally, in order to prevent the gelatine from easily 

 running off it when poured out. The apparatus consists of 

 a levelling- stand in the shape of a wooden triangle with 

 feet formed by levelling- screws, upon which rests a rather 



Bell-glass 



Thick plate of MiH llH^Hilk ^ -- ' Glass P late 



glass 



Levelling screw 

 Levelling stand 



FIG. 16. LEVELLING APPARATUS FOR MAKING PLATE-CULTIVATIONS. 



large glass dish filled with water and pieces of ice and 

 covered with a thick glass plate or a sheet of iron. The 

 latter having been brought into a horizontal position with 

 the help of a spirit-level, glass plates to receive the 

 gelatine can be laid upon it and protected with a bell-glass 

 (fig. 16). 



Moist chambers are employed for the further carrying 

 out of the cultures } they are made of glass, and have a 

 diameter of about 24 cm. and a height of 6 to 7 cm. (see 

 p. 56). 



Instead of the ordinary glass plates, which are the size 

 of a photographic quarter-plate, round glass dishes are 

 also used. Petri's capsules consist of flat double dishes of 

 glass, of which the lower has a diameter of 10 cm. 



