The faculty of the algae to produce bacteriostatic substances is commonly known (KoRZYBSRI & KURYIowICZ, 1959). Since WARS-MAN et al. (1937) noticed that :`. . . in the presence of living culture of Nitzschia . . . the bacterial activities were very limited ', and PRATT et al. (1944) pointed to the fact that Chlorella produces the antibiotic chlorellina pronouncedly checking the growth of bacteria, very few new observations had been published in this respect. Ultimately STARMACH (1955) reported that : 'Anabaena fins aquae and Microcystis aeruginosa .
among others, in a mass development 'yield substances rendering impossible or checking the life of other algae', and STEEMANN NIELSEN (1956) reports that : `Antibiotics produced by the plankton algae in light reduced the bacterial activity', reducing by the same biochemical oxygen demand of water in light . STANGEN-BERG (1964) reported bacteriostatic effects of extracts from Aphanizomenon flos aquae and Microcystis against 6 species of bacteria .
As shown by the bibliography : 1 . The bacteriostatic role of many species of algae has not been examined at all, 2 . The conceptions of bacteriostatic and toxical influence of algae have been confused, 3 . It is not clear whether in all cases the bacteriostatic effect was due to extracellular substances of the algae that have been excreted into water or whether they come from dead algal cells, in natural state or after they had been triturated and extracted .