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tion. These plastic filter sheets, when used with suction filtration apparatus, 

 make it possible to filter large volumes of water very rapidly and to remove sus- 

 pended matter down to a fraction of a micron. The filters can be dried, and by 

 the addition of appropriate liquids can be rendered optically clear, so that the 

 whole filter can be placed under a microscope for observing or counting the sus- 

 pended material. There are many obvious applications of these. 



While the tendency nowadays is for the development of complicated and 

 precise instruments which, to be sure, are making available a fund of new infor- 

 mation, nevertheless we have to keep in mind that these are expensive and in 

 many parts of the world oceanographers will for a long time be limited to the 

 older methods which use simple, everyday apparatus. In our enthusiasm for 

 automatic and precise instrumentation we must not lose sight of the opportunities 

 for improving old methods. 



