176 



BACTEEIOLOGY; 



ground plate of the ice apparatus, and cover with the bell- 

 jar. As soon as the plate is cool, it is ready to receive the 

 gelatin. Before pouring the contents of a tube upon a 

 plate; it is necessary, as a matter of precaution, to sterilize 

 the neck of the tube. This is easily accomplished, in the 

 following manner: Remove the cotton plug from the tube 

 (No. 1), and rapidly rotate the neck of the tube in the 

 flame. This is thus sterilized, and the contents of the tube 

 ■can now be poured, without coming into contact with for- 

 eign organisms. In about a minute, the neck of the tube 

 is sufficiently cool to proceed. Raise the bell- jar some- 

 what, shielding the plate as much as possible from draughts 

 of air, and pour the gelatin on the center of the plate. 

 With the lip of the tube, rapidly spread the gelatin over 

 as much of the surface as possible, avoiding, however, the 

 edges of the plate. The plate is now allowed to remain 



under the bell-jar 

 till the gelatin be- 

 comes solid. The 

 empty gelatin tube 

 should not be placed 

 on the table but 

 should be set in a 

 tumbler. When 

 through plating, all 

 the empty tubes 

 should be sterilized, 

 either by immersion 

 in mercuric chlo- 

 ride, or better by 

 exposure to boiling water or to steam. 



While the gelatin on the plate is becoming solid, a 

 ' ' moist chamber " is prepared in the same way as for potato 

 cultures (p. 167). It is not necessary to sterilize, either the 

 moist chamber, or the glass benches on which the plates 

 are to be placed. Instead of mercuric chloride, tap-water 



Fig. 31. Ise apparatus for cooling gelatin plates. 



