38 LABORATORY GUIDE IN BACTERIOLOGY 



completely immersed in the water. The culture-tubes 

 are then slipped in, and the water is heated to 100. 



3. Singe the cotton stopper of the liquefied agar- 

 tubes in the flame, remove the cotton stopper, pass the 

 mouth and about one inch of the tube through the flame, 

 and pour the contents into a sterile Petri dish, carefully 

 lifting the cover (Fig. 21) and quickly replacing it. 



4. Repeat this operation with the second agar-tube. 



5. Place both Petri dishes containing the liquid agar 

 on a level surface. 



6. When the agar is solidified, expose, by removing 

 the cover, one dish to the air of the laboratory, and the 

 other outside on the window-sill, for 10 minutes. 



FIG. 21 

 Pouring Medium into Petri Dish 



7. Replace the cover and place in lockers. 



8. Cool the water-bath to 43 exactly, and mix the 

 scrapings from under a finger nail with the liquid glucose- 

 agar. Keep this also in the locker. 



9. Remove the plug of a tube of broth and place a 

 hair in the liquid. Keep also in the locker. 



When inoculating liquefied agar media, it is necessary 

 to do so at a temperature no higher than 43 nor lower 

 than 40. Above 43 the organisms are liable to be 

 injured by heat; below 40 the agar solidifies, and an 

 even distribution is impossible. If gelatin is used, the 

 latter precaution is not imperative, as gelatin solidifies at 



