medical schools. Detailed knowledge of equipment and the related physical laws has gained increasing importance in the training of anaesthesiologists. Fundamental knowledge of the design, function, and performance of an anaesthesia machine is the key to the art of its use. Mainz/Rhine, December 1971 Dr. RUDOLF FREY, F.F.A.R.C.S. Professor of Anaesthesiology Johannes Gutenberg-University Acknowledgements I wish to thank Dr. STANLEY W. WEITZNER, Professor, Department of Anesthesiology, State University of New York, Downstate Medical Center, for his helpful criticism of the chapter dealing with the per­ formance and classification of ventilators. I also want to thank Mr. DAVID F. BOERNER for his assistance in rewording the language and physiochemical terminology of the manu­ script.