Silicon chemistry was initiated in 1823 by Berzelius who prepared elemental silicon. In many ways silicon was considered a typical opposite of carbon, although the two elements are closely related as to their electronic structure, both having four valence electrons. The properties of their compounds are, however, extreme ly different. Both form extended structures, but in different ways - carbon by covalent carbon-carbon bonds; silicon by polar silicon- -oxygen-silicon bonds. The complex carbon compounds are integral parts of all living matter, plants and animals. The corresponding silicon compounds build up a major part of dead matter, soils and minerals. As recently as twenty years ago the title of this Symposium, "BiOChemistry of Silicon", would have been considered as contradictio in adjecto. However, the development in the field has, during the past fifteen years, been overwhelming and has convinced us that silicon is a necessary element in the life processes, for animals as well as for plants. Interesting therapeutical uses have been suggested, but we have also become increasingly aware of serious occupational diseases - asbestosis and silicosis - and of possible cancerogenic effects. It is our hope that this volume will give some idea about various aspects of silicon compounds which were discussed during the Symposium.

Inhalt
General Chemistry of Silicon.- Aqueous Silicic Acid, Silicates and Silicate Complexes.- Hydrogen-Bonded Complexes of Silica with Organic Compounds.- The Silicon-Nitrogen Bond. A Short Survey.- Silicon in Soil, Plants and Microorganisms.- Effect of Interactions of Silicious Components and Organic Substances on Life in Soil A Contribution to Plant Production.- Isolation and Characterization of a Silicon-Organic Complex from Plants.- Biodegradation of Silicon-Oxygen-Carbon- and Silicon-Carbon-Bonds by Bacteria A Reflection on the Basic Mechanisms for the Biointegration of Silicon.- Regulation of Metabolism by Silicate in Diatoms.- Role of Silicon in Diatom Metabolism and Silicification.- Physiological Significance of Silicon Compounds in Animals and Man.- Significance and Functions of Silicon in Warm-Blooded Animals. Review and Outlook.- Essentiality and Function of Silicon.- Silicon Levels in Human Tissues.- Silicon, Endocrine Balance and Mineral Metabolism (Calcium and Magnesium).- The Physiological Role of Silicon and Its Anti-Atheromatous Action.- Isolation and Characterization of a Characteristic Phosphato-Silicate from Human Lungs with Silicosis.- Silicosis and Other Diseases Caused by Silicon Compounds.- Carcinogenic Potential of Silica Compounds.- Interactions of Silica and Asbestos with Macrophages.- Cellular Reactions with Silica.- Old-New Problems of Silicotic Fibrosis.- Biological and Pharmacological Effects of Organo-Silicon Compounds.- Biological Activity of Silatranes.- Biological Activity of Nitrogen-Containing Organosilicon Compounds.- Silica-Pharmaca.- The Pharmacology of Silanes and Siloxanes.- Biochemical Effects of 2, 6-cis-Diphenylhexamethyl-cyclotetrasiloxane in Man.- Structural and Analytical Aspects of Organosilicon Compounds.- StructuralAspects on Organosilicon Compounds.- Analysis of some Organosilicon Compounds in Biological Material.- Discussion and Summary.- Silicon in Biological Systems.- Final Discussion.- List of Participants.