Reports and Reviews: Book Review: ANAEROBIC DIGESTION: PRINCIPLES AND PRACTICES FOR BIOGAS SYSTEMS (Integrated Resource Recovery Series, UNDP Project Management Report, No. 5; World Bank Technical Paper, No. 49). By Charles G. Gunnerson and David C. Stuckey, The World Bank, Washington, DC, xv + 154 pp., 1986. Price $8.00 U.S.A. Reviewed by C. Polprasert and S. Mya