122 



A MANUAL OF BACTERIOLOGY 



FIG. 41. Filtering apparatus 



Air is pumped into the tank and furnishes pressure to force the solution 

 through the filters 



rubber tubing, which should be wired on. Turn on the air slowly 

 until a pressure of 15-20 pounds is exerted. The liquid should 

 drip rapidly from the bougie, but an excess of pressure should be 

 avoided, because small organisms might be forced through the wall 

 of the filter 



