INVISIBLE MICROORGANISMS 



117 



-Fig. 89. — Apparatus for fractional filtration, designed for use with Pasteur- 

 Chamberland or Berkefeld filters. 0, Glass mantle surrounding filter; 6, Chamber- 

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

 g, pinchcock controlling outlet from suction flisk; 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 inlettube 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. Deft, oj Agri- 

 culture, Bureau of Animal Industry, Bu'l. 113.) 



