196 MICROSCOPIC AND CULTURAL STUDY OF BACTERIA 



It is necessary to burn the surface of the plug to destroy surface con- 

 tamination, then to push the plug into the neck of the flask for a dis- 

 tance of 1 cm. to make room for the paraffin. Flasks hermetically 

 sealed in this manner may remain visibly unchanged for weeks or even 

 months. It is good practice to place a lead foil cap over the paraffin 



FIG. 22. Autoclave. (Park.) 



plug and lead foil caps are better than paper caps as coverings for cot- 

 ton plugs. Media in storage should be maintained at a temperature 

 not exceeding 45 C., in a dry ice-box. 



The Preparation of Nutrient Bouillon (Broth). M eat Infusion Broth 

 To 1000 c,c. of meat infusion (see page 189 for preparation), in a tared, 



