by Waldemar C. Dreessen, passed assistant surgeon, J.M. Dallavalle, passed assistant sanitary engineer, Thomas I. Edwards, technical editor, R.R. Sayers, senior surgeon, United States Public Health Service, and H.F. Easom, M.D., director, M.F. Trice, engineer, Division of Industrial Hygiene, North Carolina State Board of Health ; from the Division of Industrial Hygiene, National Institute of Health ; prepared by direction of the Surgeon General