Laboratory Outline for General Bacteriology 



amount of the material to be tested is mixed with the fluid agar 

 and allowed to cool. Each bacterium is held in a certain spot on 

 the agar. Bacterial colonies develop upon several days incubation 

 and each colony represents one bacterium or clump of bacteria 

 originally present. 



Agar itself is not a food for microorganisms. Its special value 

 is in hardening media used for cultivating organisms which grow 

 at a temperature above melting point of gelatin. This feature 

 has made possible the great strides that have been taken in medical 

 bacteriology. 



TO DETERMINE THE MELTING AND SOLIDIFYING POINTS 

 OF AGAR AND GELATIN 



Place tubes of agar and gelatin in wire basket. 

 Set in pan with water above level of media in tubes. 

 Insert thermometer in gelatin. 

 Place pan over gas flame and watch thermometer. 

 When liquefied record temperature. 



Change thermometer to agar tube and record melting temperature. 

 Flace tubes in cold water and watch for solidifying point first of 

 agar, then of gelatin. 



Melting point Solidifying point 



Agar C. C. 



Gelatin C. C. 



AIR ANALYSIS 



Sterile melted agar tubes will be furnished. Pour seven into 

 Petri dishes using one tube to a dish. In doing this remove cotton 

 stopper without touching end of tube. Raise one side of the cover 

 of the dish just enough to allow the pouring of the agar. This is 

 done to prevent bacteria dropping in from the air. When agar is 

 solid expose plates with cover removed for five minutes in the 

 places designated below. Keep cover right side up while off from 

 plate. The one out of doors should be taken away from roads or 

 buildings. Face the wind in exposing plate so that bacteria will 

 not below from you onto the plate. With red glass marking pencil 

 mark the plates with your name, the date, and place of exposure. 

 After exposing plates place in locker inverted to incubate. 



18 



