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MORPHOLOGY AND CULTURE OF MICROORGANISMS 



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

 Chamberland or Berkefeld niters, 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 nitrates 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, Butt. 113.) 



