Professor B.G. WEBER has once again and in a very timely fashion produced a superb book on an orthopaedic subject of great importance. "The Extemal Fixator" is the most comprehensive text on the subject in orthopaedic literature to date. Professor WEBER thoroughly discusses extemal fixation with c1arity, organization, profuse illustrations and roentgenograms. Professor WEBER acknowledges that the use of extemal fixation in orthopaedic surgery is not newand traces its history over the years. He points out c1early the fact that though at various times the "method" has experienced periods of disrepute, modem sophistication, improved technology and a better understanding of its philosophy have given the system a newand perhaps permanent place in the armamentarium of the orthopaedic surgeon. All methods of treatment have critics as well as supporters, and not infrequently the strongest criticisms are the result of poor understanding of the philosophy proposed and its proper implementation. Professor WEBER, in his carefully detailed and well illustrated book, has made it abundantly c1ear that the use of extemal fixators in the treatment of fractures must be c1early understood by the orthopaedic surgeon in order to obtain satisfactory clinical results. His discussion of its philosophy, pathomechanics and technology are most comprehensive and leave "no stone untumed" and because of this the book represents a most comprehensive text on the subject.

During their 20 years of activity members of the Associa tion for the Study of Internal Fixation (AO - ASIF) have made authoritative contributions to the development of internal and external fixation. The close collaboration of surgeons, basic researchers, metallurgists, engineers and the establishment of clinical documentation has made it possible to achieve a solid scientific basis for internal fixa tion. Clear definitions for the standardization of different types of osteosynthesis were possible: interfragmentary compression, splintage and buttressing as well as combina tions of these three techniques. At the same time a scienti fic and workmanlike instrumentation was developed. The idea was to keep diversification within limits but, however, to assemble a comprehensive collection of implants and in struments to answer all the problems presented by the com plexity of bone operations. Osteosynthesis is a difficult and demanding operative method. Its. claims on the surgeon and the theatre staff are high. Therefore plans have existed for a long time to supplement the "Manual of Internal Fixation" with a de tailed description of the AO Instrumentation, its use and maintenance. Our collaborator FRIDOLIN SEQUIN, graduate engineer, has accomplished this task with expert knowledge. He has organized over many years courses for theatre nurses and has been able from the resulting experience to provide helpful suggestions. When RIGMOR TEXHAMMAR R. N. joined AO-International four years ago, it was natural to include her as a co-author."

The octapeptide angiotensin II (ANG II, Fig. 1) is the key effector substance of the renin-angiotensin system (RAS) (Werning 1972, Page and Bumpus 1974, Hierholzer 1977, Vecsei et al. 1978, Johnson and Anderson 1980 lit. ). ANG II is formed in two enzymatic steps. Renin acts on renin substrate, a glycoprotein, to produce angiotensin I (ANG I, a decapeptide), which in turn is acted upon by converting enzyme to form ANG II (Skeggs et al. 1968, Fig. 1). Renin substrate (angiotensinogen) is produced mainly in the liver (Page et al. 1941) and is a constituent of the ~-globulin fraction in the circulating plasma (Plentl et al. 1943). The two enzymes involved in the formation of ANG II from renin substra- te are formed at various sites in the body. Renin (E. C. 3. 4. 99. 19) is produced mainly in the granular epithelioid cells of the kidney (Cook 1971, Taugner et al. 1979, Davi- doff and Schiebler 1981), and converting enzyme (CE, E. C. 3. 4. 15. 1) occurs chiefly in the lung (Ng and Vane 1967, Bakhle 1974 lit. ) as well as in numerous other tissues, such as the juxtaglomerular apparatus of the kidney (Granger et al. 1969, 1972) and the brush border of the renal proximal tubule (Ward et al. 1975, 1976; Ward und Erdos 1977). The biological effects of ANG II are numerous.

Functionally stable internal fixation is of particular relevance to maxillo facial surgery, because it obviates the discomforts and inconveniences of intermaxillary fixation. Given the biomechanics and biophysics of the skeletal system, the true im mobilization of bone can be achieved only through highly technical means. Willenegger speaks of an "advanced school" of bone surgery which, when fully realized, will enable excellent results to be achieved even in the most difficult fractures. To accomplish this goal, ongoing refinements are needed in surgical methods and technology. Advancing the state of operative tech nique has been a central concern of the Association for the Study of Inter nal Fixation since its establishment 25 years ago. For this reason, a major priority of the AOI ASIF has been to develop its own surgical instrumen tation. With the help of technical commissions comprised of experts from medi cine, research and manufacturing, the AOI ASIF has been able to develop and successfully test a line of surgical instruments whose trademark is known and respected the world over. For every specialty in traumatology and orthopaedics, including maxillofacial surgery, the AOIASIF has devel oped both a basic and a special instrument set designed to meet specific anatomic requirements."