IN MEMORIAM ZAVIS CYRUS PROFESSOR ZAVIS CYRUS, President of the Czechoslovak Limnological Society, died in Prague December 19, 1971 at the age of 64 years . ZAvIS CYRUS was born March 4, 1907 in Libenice (nr Kolin, Bohemia), completed his studies of natural history and athletic education at the Charles University in 1932 and specialized in phycology as student of PROFESSOR DR . J . VILHELM . After more than 10 years of teaching at various grammar schools in Bohemia he was appointed phycologist-hydrobiologist in the Water Research Institute in Praha-Podbaba (1944) . Together with his elder brother BOHUMIL CYRUS (obituary in Hydrobiologia 25 : 586-587, 1965) and with RUDOLF SRAMEK-HUSEK (see Hydrobiologia 21 : 384-389, 1963) he became one of the founders of Czechoslovak applied hydrobiology .
Besides a few earlier papers on floristics of algae and on the diatoms accompanying the Oscillatorietum (1948), he became coauthor of the first map of water quality (1947) covering the rivers in Bohemia and Moravia and using the classical system of KOLK-WITZ & MARSSON . This was the first map of this type in the world .
He developed a counting chamber for phytoplankton and organisms of activated sludge which carries now his name . It is an enlarged haemacytometer with an area of 100 mm 2, height 0,1 mm and volume 0,1 ml . A grid enables the enumeration of the organisms .
He made a classification of the macroscopic as well as microscopic flocks of activated sludge (1969) and identified several very interesting organisms among colorless algae, filamentous bacteria and flexibacteria . His only paper published abroad (1970) was that in Hydrobiologia .
Z . CYRUS introduced a physiological test of toxicity distinguishing living and killed cells of a filamentous green alga (either Cladophora glomerata status stagnalis or Rhizoclonium hieroglyphicum) . Bubbles of oxygen produced during photosynthesis rise the algal clump to the water surface in a cylinder, whereas the killed algae lie on the bottom and subsequently undergo decomposition .
The term antisaprobity, characterizing a toxic, abiotic degree in water quality was proposed by him (1947) .