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AGAR PLATE CULTURES. 



The ordinary gelatin plates are applicable for the 

 isolation of colonies of only those organisms which can 

 grow at ordinary room temperature. Above 25 C. the 

 nutrient gelatin melts and cannot therefore be employed 

 as a solid medium for the growth of those organisms which 

 develop only at a higher temperature. In such cases plates 

 can be made with ordinary, or glycerine or glucose agar. 

 The method of making agar plate cultures is briefly as 

 follows: 



Three agar tubes are immersed in boiling water in a 

 water-bath until the contents are liquefied. The burner is 

 then removed from under the water-bath and the water 

 with the immersed tubes is allowed to cool slowly until a 

 temperature of 45 C. is reached. Tube 1., is inoculated 

 with the material to be plated and the usual dilutions to 

 tubes 2 and 3 are made as rapidly as possible. The cotton 

 plugs are then cut off short, pushed in slightly, and the 

 lips of the tubes sterilized in the flame. The inoculated 

 contents are then poured into sterilized Petri dishes, or on 

 ordinary sterilized plates. Inasmuch as the agar solidifies 

 at about 40 it will require rapid work to inoculate the 

 tubes and pour the contents before solidification takes 

 place. Ice-water must not be used to congeal the agar. 

 The Petri dishes or plates are then placed in the incubator. 



Esmarch roll-tube cultures can also be made with 

 agar in the same manner as described for gelatin cultures. 

 The tubes should be rotated in ordinary tap water. 



LABORATORY WORK. Make glycerine agnr Petri 

 dishes from the spleen of a guinea-pig inoculated with 

 glanders. When the colonies develop, make streak cul- 

 tures on inclined glycerine ngar. Examine the spleen and 

 also the pure cultures in the usual manner by making 

 hanging-drops and cover-glass preparations. 



