62 



ESSENTIALS OF BACTERIOLOGY. 



FlG. 31. 



A 



Iron box for glass plates. 



Glass Plates. The larger the surface over which the nutrient 

 medium is spread the more isolated will 

 the colonies be ; window glass cut in rec- 

 X^N tangular plates Gx4 inches in size is used ; 



S^j/J Vs^"/) about ten such plates are cleaned with dry 

 towel and placed in a small iron box or 

 wrapped in paper ; and sterilized in the 

 hot-air oven at a temperature of 150 C. 

 for ten minutes. (Fig. 31.) When the 

 plates have cooled they are placed upon 

 an apparatus designed to cool and so- 

 lidify the liquid media, which is now 

 poured upon the plates from the inocu- 

 lated test-tubes. 

 Nivellier Leveling and Cooling Apparatus. Ice and water 

 are placed in a shallow round glass tray ; on top of this a square 

 plate of glass, upon which the culture plate is placed, and cov- 

 ering this a bell-glass. 



The whole is upon a low, wooden tripod, the feet of which 

 can be raised or lowered, and a little spirit-level used to adjust 

 it. (Fig. 32.) The glass plate taken out of the iron box is placed 

 under the bell-glass. The tube containing the gelatine is held 

 in the flame a second to singe the cotton plug to free it from dust, 

 and the plug removed, the edges of the tube again flamed, the bell- 

 glass lifted, and the inoculated gelatine carefully poured on the 

 plate, leaving about one-third inch margin from the borders ; the 



FIG. 32. 



Nivellier leveling and cooling apparatus. 



lips of the tube being sterile can be used to spread the media 



