PREPARATION OF NUTRIENT MEDIA. 



39 



of the box there are openings to admit a thermometer 

 and a thermo-regulator, which are passed through 

 tight-fitting corks. The apparatus is now heated with 

 Bansen burnerSj two, three, or four, according to the 

 size of the box, until the required temperature is 



Pig. 3. 



obtained. If gas is not available, a smaller apparatus 

 may be heated with specially constructed petroleum 

 lamps. 



The test-tubes and cotton- wool are completely steri- 

 lised if they are kept in this apparatus for three hours 

 at a temperature of 140°-160° C. This method is called 



