THE CURTAIN WALL--"The term 'curtain wall' is used nowadays to describe the sheath, or 'skin,' of a modern building. It looks quite different from its predecessor, the old load-bearing wall, and in fact it represents a big advance in architectural evolution. The structural specialization involved in separation of the skin and the skeleton in a building corresponds to the specialization of tissue in biological evolution. Yet no building skin today approaches the performance of the biological world. The curtain wall is passive, lacking the power to adjust to the fluctuating external environment. It should be able to intervene actively in the building's struggle to maintain its internal stability. --James Marston Fitch"