L-------------------------------------------~ Kathy Ruppel, Ken Niebling and JeffFiner for their help and comments on the first draft. I am also grateful for discussions with and comments from Dr Neil Miliar, Professor Bob Simmons, Dr Roger Cooke, Dr Tosbio Yanagida, Dr John Kendrick-Jones, Dr Rob Cross, Dr Ian Trayer, Dr John Sparrow, Dr Michael Geeves, Dr Bernhard Brennerand Dr Peter K. night. The task of illustrating the book was made much easier by the photographs and diagrams kindly provided by Professor Ken Holmes, Dr Ron Milligan, Professor Basil Northover, Dr Hans Warrick, Dr John Squire, Dr JetT Harford, Dr Mary Reedy, Dr A vril Somlyo, Dr Darl Swartz, Dr Marion Greaser, Dr Peter Knight, Dr Gerald OtTer, Dr Roger Craig, Dr Peter Vibert, Dr John Kendrick-Jones, Dr Andrew Jackson, Dr Don Winkelmann, Dr Andrew Sowerby and Dr Richard Ankrett. I am grateful to the Science and Engineering Research Council for funding my travel to Stanford University. Permission to reproduce copyrighted material from the following publishers is gratefully acknowledged. The Physiological Society (Figs 2. 6, 6. 1, 6. 11, 6. 12, 7. 6), The RockefeBer University Press (Figs 3. 5, 4. 8, 8. 3), Academic Press(Figs3. 4,4. 4,4. 15, 9. 1, 9. 2), MacmillanPress(Figs 4. 2, 4. 3, 4. 12, 4. 13, 6. 6, 6. 9, 7. 8, 9. 3), Longman Group (Fig. 6. 7), The Royal Society (Fig. 3. 7) and D. W. Fawcett (Fig. 3. 1).