GENERAL BACTERIOLOGY 71 



contents into a sterile petri dish, carefully lifting the 

 cover (Fig. 26) and quickly replacing it. 



4. Repeat this operation with the other tubes, 

 excepting glucose agar. 



5. Place all petri dishes containing the liquid agar 

 on a level surface. 



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

 the cover, one dish of plain agar and one of wort agar 

 to the air of the laboratory, and the other two outside 

 on the window-sill, for 5 minutes. 



7. Replace the cover and place in incubator. 



FIG. 26 

 Pouring Medium into Petri Dish 



8. Cool the water bath to 43 C., and mix the 

 scrapings from under a finger nail with the liquid 

 glucose agar. Incubate at 37 C. 



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

 hair in the liquid. Incubate at 37 C. 



Liquefied agar media should be inoculated at a 

 temperature no higher than 43 C. nor lower than 40 C. 

 Above 43 C. the organisms are liable to be injured 

 by heat; below 40 C. the agar solidifies, and an even 

 distribution is impossible. If gelatin is used, the 

 latter precaution is not imperative, as gelatin solidifies 

 at about 25 C. 



Observe and make notes on the appearance of these 

 petri dishes after 24 hours. By this time it will be 



