Includes "References cited." Microbiota of sewage treatment plants and polluted streams, by J.N. Wilson.--Some epidemiological and biological problems in water-borne amoebiasis, by S.L. Chang.--Biotic responses to stream pollution during artificial stream reaeration, by A.F. Bartsch and W.S. Churchill.--A study of kraft pulping wastes in relation to the aquatic environment, by W.M. Van Horn.--Plankton as related to nuisance conditions in surface water, by J.B. Lackey.--Preliminary studies on the viability and dispersal of coliform bacteria in the sea, by B.H. Ketchum, C.L. Carey and Margaret Briggs.--The algologists' part in city and industrial water supply problems, by C.E. Taft.--The use of copper sulphate for algal control and its biological implications, by J.B. Moyle Gift of B.H. Ketchum