DIRECT EXAMINATION 



39 



FIG. 4. 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 

 contamination when the filtrates are drawn off;.;, glass inlet tube plugged with cotton, 

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

 into flask; /, vacuum gauge; m, stopcock connected with vacuum pump. (U. S 

 Dept. of Agriculture, Bureau of Animal Industry, Bull. 113.) 



