S64 FILTERABILITY OF MICRO-ORGANISMS 



both cases the surfaces of the pores of the filter are ''insulated" or their charge is 

 neutralized and so cannot influence the charged particles passing through the filter. 

 When the filters are "cleaned" by running through them alcohol followed by ether, 

 they regain their power of removing colloid dyes of opposite charge. I have tried to 

 picture the action of the two kinds of filters in Figures i and 2. 



It may be asked, "What influence has the reaction of the medium on the filtera- 

 bility or non-filterability of suspended particles or colloids?" In general, it may be 

 answered that, assuming that the charge of the filter remains unchanged, whenever 

 a change in the reaction of the medium brings about a change in the charge of the 

 particle or colloid then will the filterability or non-filterabihty be changed; other- 

 wise not. 



