Molecular biology has now advanced to the point where it is no longer possible to give a complete review of the available data on the conformational features of proteins. New data keep streaming in, and there is obviously an urgent need for some sort of general treatment of the subject. A systematic treatment of the large amount of data obtained by a great variety of methods on a great variety of objects must be based on the use of models; these should be as simple as possible, should conform to well-established scien tific laws, and at the same time be sufficiently flexible. The validity of...