Harvard University, Cambridge, Massachusetts/Commonwealth Fund Book, 1982, 4^th pr.  ISBN 0-674-13581-4.  Trade soft cover, 448 pages including Glossary, References and Index.  Good plus; wraps have some edge and cover wear, reading creases; binding sound.  Interior clean with some pencil underlines, marginalia and check marks.  ‘Jet lag, insomnia, the night shift, sleeping pills - outside events often disrupt sleeping patterns and the rhythm of our daily lives.  Science has only recently begun intensive study of how our bodies are timed by internal clocks and how we accommodate when another schedule is imposed on our personal periodicity.’ (from rear wrap)