I2O 



MORPHOLOGY AND CULTURE OF MICROORGANISMS 



a 



FIG. 90. Apparatus for fractional filtration, designed for use with Pasteur- 

 Chamberland or Berkefeld filters, a, Glass mantle surrounding filter; b, Chamber- 

 land filter; c, paraffin joint; d and e, rubber stoppers;/, double side-arm suction flask; 

 g, pinchcock controlling outlet from suction flask; h, outlet tube surrounded by glass 

 shield and attached to lower end of suction flask by means of short rubber tubing; 

 i, glass shield fused to and surrounding outlet tube as a protection against contamina- 

 tion when the filtrates are drawn off; j, glass inlet tube plugged with cotton, for ad- 

 mitting air into suction flask; k, pinchcock governing the admission of air into flask; 

 I, vacuum gauge; m, stopcock connected with vacuum pump. (U. S. Dept. of Agri- 

 culture^ Bureau of Animal Industry, Bull. 113.) 



