30 LABORATORY BACTERIOLOGY 



their appearance. The notes should contain a detailed record 

 of the cultures made in this exercise. 



Read carefully the paragraphs in the text-books on making 

 plate and roll cultures. 



43. Making agar plate cultures. Take 3 large tubes of 

 agar, stand them in a water bath, and boil until the agar is 

 liquefied. Then cool by standing the tubes with a thermome- 

 ter in a cup of water at a temperature of about 50° C. As the 

 temperature rises, add a little cold water. When the tempera- 

 ture of the agar reaches that of the water, and the temperature 

 of the whole has lowered to 40° C, the agar is ready for use. 

 For convenience in labeling, number the tubes i, 2, and 3. 



Place 3 sterilized Petri dishes on the leveling tripod and 

 adjust it by means of a spirit level. With the wire loop pro- 

 ceed by the same method as followed in making bouillon 

 cultures. Take one loopful of the bouillon culture, place it 

 in agar tube i and mix by carefully shaking. Flame the 

 wire and transfer 2 loopfuls of agar from tube i to tube 2 

 and mix as before. Again flame the loop and transfer 3 loop- 

 fuls from tube 2 to tube 3 and mix as with tubes i and 2. 

 After the tubes are inoculated, pour the agar into the Petri 

 dishes. In doing this remove the plug, carefully flame the 

 mouth of the tube, and after quickly cooling, raise with the 

 left hand the edge of the cover on one side of the Petri dish 

 sufficiently to allow of inserting the mouth of the tube. After 

 the agar is poured out of the tube replace the cover immedi- 

 ately. Label and number the Petri dishes to correspond with 

 the dilutions in the tubes : thus, plate i is from tube i , plate 2 

 is from tube 2, and plate 3 is from tube 3. Place the label 

 near the edge of the cover. The Faber pencil for marking 

 glass may be used instead of the gummed label. In making 

 the dilutions it is important that the wire loop should be 

 flamed after making each transfer. 



44. Making gelatin plate cultures. These are prepared 

 precisely as the agar plates, with these exceptions : (i) the 



