“…MEMBRANE FILTERS have been employed in a variety of bacteriological techniques including viable counting (Clark, Geldreich, Jeter & Kabler, 1951), sterility testing (Holdowsky, 1957) and the investigation of bactericidal activity (Shipe & Fields, 1954; Harris & Richards, 1958; Hess & Speiser, 1 9 5 9~~6 ) .…”