Here the phrase 'tumor genesis' refers chiefly to the material and formal genesis of tumors; their etiology, or causal genesis, is not an issue. The questions are, from what component of the body, whether fluid or solid, are tumors derived, and what are the factors determinative of their gross and microscopic structure? This book is an attempt to show that a thread of logical continuity runs through the long history of Western medical thought on the genesis of tumors. In the first chapter, changing ideas of the genesis of tumors during the past two thousand years of the Western medical tradition are reviewed. The second chapter gives an account of the development of knowledge of the fine structure of animal bodies which culminated in the rise of tissue theory at the end of the eighteenth century and its application to the problem of tumor genesis in the beginning of the nineteenth century. The third chapter is devoted to the study of the structure and genesis of tumors in the light of Schwannian cell theory in Germany in the 1840s and the fourth chapter details the overthrow of Virchow's concept of the connective-tissue genesis of epithelial cancer some twenty years later. The fourth chapter does not carry the story past the 1880s because the presuppositions underlying the inferences drawn from this cumulative evidence underwent little significant change during the subsequent seventy to eighty years. Only in very recent times have techniques been introduced that shed new light on the genesis of tumors. -- from Preface and Introduction