28 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. 



41 . Making Agar Plate Cultures. — Take three 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 tempera- 

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

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



Place 3 sterilized Petri dishes on the levelling 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 cul- 

 tures. Take i loopful of the bouillon culture and place it in 

 agar tube No. i and mix by carefully shaking it. 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 suffi- 

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

 agar is poured out of the tube replace the cover immediately. 

 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. In making the dilu- 

 tions it is important that the wire loop should be flamed after 

 making each transfer. 



42. Making Gelatin Plate Cultures. — These are prepared 

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

 gelatin is liquefied at a temperature of 45° C. (2) The plates 

 when made are to be kept in the locker the same as the gelatin 



