This book is intended for students of biochemistry, biology, and medicine who are familiar with textbook knowledge of intermediary metabolism. Present-day graduates however, are often unaware of the contributions made to this knowledge by the great biochemists in the earlier part of this century. We hope this volume will help to correct this deficiency and strengthen interests in these pioneers. We have also tried to show how our present information about some of the central pathways in animals was obtained, describing the limited experimental techniques which were available and indicating how advances in methodology opened up new areas of the subject which were then enthusiastically explored. The account covers the period from 1900 to 1960, but also outlines the principal developments in earlier centuries from which biochemistry emerged. We have not attempted a rigid historical treatment; the findings are considered in the light of our present knowledge.