PLATE CULTURES. 69 
5. Shake the third tube, and pour the contents 
of the three tubes into sterile Petri dishes, having 
first passed the lip of each tube through the flame. 
6. On the surface of the first Petri dish, before 
4 
Fic. 44.—The various appearances of colonies of bacteria 
under the microscope: a, colony of Bacterium parvum ; 
4, colony of Bacillus polypiformis ; c, colony of Bacillus 
radiatus. 
the medium has entirely solidified, press a sterile’ 
cover-glass or small piece of mica. 
candle-powers from five to thirty. By adjusting the socket 
to the different candle-powers the requisite temperature of 
water or paraffin is secured and indicated by the thermom- 
eter. When used as a water-bath, the dish is provided 
with a wire rack to support the tubes to be melted. When 
used for paraffin, little baskets of wire gauze, containing the 
specimens to be embedded, are hung about the sides. It 
is convenient to have the water-bath kept at a temperature 
of 40° C. In this gelatin-tubes may be melted, or agar- 
tubes, after being melted at a higher temperature, may be 
cooled down and kept melted until used. 
1Sterilize by heating in the flame. Allow it to cool before 
placing on the plate. 
