RESISTANCE TO LETHAL AGENTS 



307 



4. Spread the suspension in thin, even films on 

 sterile cover-slips and deposit inside sterile "plates" 

 to dry. 



5. As soon as dry, transfer the cover-slip films to the 

 ventilated Petri dish by means of sterile forceps. 



w 



FIG.. 157. Mueller's desiccator. 



6. Place the Petri dish inside the Mueller's desiccator; 

 fill the upper chamber with pure sulphuric acid, cover 

 with the bell jar, and exhaust the air from its interior. 



FIG. 158. Petri dish for drying cultivations. 



Ten minutes later connect up the desiccator to a 

 sulphuric acid wash-bottle interposing an air filter so 

 that only dry sterile air enters. 



