With the exception of this Preface and the Introduction, the present volume consists of selections from material previously published in books or professional journals. With each piece is included a source note that gives the full bibliographic reference of the original work and acknowledges those who granted permission to use the material. In the case of articles, the degree of completeness versus abridgement is indicated by the phrases “reprinted from,” “reprinted with minor abridgements,” “reprinted with abridgements,” and “excerpted from,” in increasing order of abridgement. Book excerpts are understood to constitute only small selections from the originals. The chapter or section from which each portion is taken has been indicated in section headings within such selections. Ellipses within both book and journal selections are used to indicate omitted portions. However, where footnotes have been deleted, no notation has been made, and the remaining notes have been renumbered consecutively.

Minor alterations in style have been made for purposes of consistency. The references have been gathered into a single listing at the end of the book, and bibliographic particulars have been added, when necessary and feasible, to make the references as complete as possible and to have them accord with the standard format of major professional journals. Reference data, except for citations of authors' names and the dates of publication, have been moved to this list from the text and notes.