Book Review: SLUDGE PARASITES AND OTHER PATHOGENS. By Robert Lewis-Jones and Michael Winkler. Ellis Horwood Ltd., Chichester, West Sussex, PO19 1EB, England, 1991, available from Prentice Hall, Simon and Shuster. 24.95, 202 pp. Reviewed by Ebba Lund, Royal Veterinary and Agricultural University, Copenhagen, Denmark