1. a Occupational Health Program, National Center for Urban and Industrial Health, U. S. Public Health Service , 1014 Broadway, Cincinnati, Ohio
2. b Perinatal Research Branch , National Institute for Neurological Disease and Blindness, Public Health Service , Bethesda, Maryland
3. c Bolt, Beranek and Newman, Inc. , Cambridge, Massachusetts
4. d Allen & Hoshall Consulting Engineers , Memphis, Tennessee