Acknowledgements This book is one of the results of the active sup port for O2MT research in the GDR given by Prof. Dr L. Mecklinger, Minister of Health, and his deputy. Prof. Dr B. Schonheit. For experimental, medical and theoretical contributions, valuable advice and help, the author is very grateful to his former and present collaborators Dr A. von Ardenne, Dr G. Bohme, Dr W. Kruger, Prof. Dr H.-G. Lippmann and Dr P.G. Reitnauer. Numerous colleagues supported the author over many years in various phases of our research by suggestions, encouragement, literature, personal advice and, last but not least, by critical check ing of parts of the German manuscript. Some of them, to whom the author is greatly indebted, should be named here: Prof. Dr H. Berg, Jena (GDR); Dr h.c. E. Braun, Engelberg (Switzer land); Prof. Dr H. Druckrey, Freiburg (FRG); Dr K. Korber, Hamburg (FRG); Prof. Dr H. Krauss (GDR); Prof. Dr W. Lubbers, Dortmund (FRG); Prof. Dr H. Schmid-Schonbein, Aachen (FRG); Prof. Dr G. Thews, Mainz (FRG); and Prof. Dr O. Westphal, Montreux (Switzerland). Finally the author wishes to express thanks for the immense help Miss Paula Kirby, Tunbridge Wells, Kent (England), has given by her trans lation. She was assisted by Dr W. Kruger, who reviewed the scientific vocabulary, but without her assistance the appearance of this book might never have occurred.