30 



36. General Directions. Make a series of 3 agar plates, 

 one of 3 gelatin plates, and a series of 3 gelatin roll cul- 

 tures (Esmarch rolls) from the bouillon culture of Bacillus coli 

 communis ( 18). Place the agar plates in the incubator and 

 the gelatin plates and rolls in a locker for that purpose. 



Re-examine all the cultures made in previous exercises 

 and add to the laboratory notes a description of any changes 

 in 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 mak- 

 ing plate and roll cultures. 



37. Making agar plates. Take three large tubes of agar, 

 stand them in a water bath aild boil until the agar is lique- 

 fied. Then cool by standing the tubes with a thermometer 

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

 temperature rises add a little cold water. When the temper- 

 ature of the agar reaches that of the water and the temper- 

 ature of the whole has lowered to 45 C. the agar is ready 

 for use. For convenience in labeling number the tubes i f 

 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 and place 

 it in agar tube No. i and mix by carefully shaking it. 

 Flame the wire and transfer two loopfuls of agar from tube 

 i to tube 2 and mix as before. Again flame the loop and 

 transfer 3 loopfuls 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, 

 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 

 dish sufficiently to allow of inserting the mouth of the tube, 

 and hold it until the agar is poured and replace it immedi- 

 ately. Label, and number the Petri dishes to correspond 



