The present study may be read and considered from different points of view: as a comparison of two authors both important for the history of medicine and biology, but with opposing conceptions of the world; as a contribution to the history of physiology from 1600 to 1850; as a study in the mechanization of the body in one of its central organs, namely the heart; as an application of the distinction between scientific discovery and fact as explained by Ludwig Fleck's theory of science on William Harvey's discovery of the circulation; and finally, as a case study on the conflict of different views, paradigms, or “thought-styles” over a longer period of the history of science.

Though I hope that the multitude of aspects to be followed will not only keep the study readable, but will even increase its attraction, a detailed introduction will try to convey the necessary overview on the topics and the course of the investigation. Moreover, summaries at the beginning of each chapter are meant to make the reader's orientation easier and to allow for a selection if necessary.

The present English edition of my book first published in Germany in 1992 would never have come to birth were it not for the insistence of Prof. Marjorie Grene, my translator and benevolent critic. I want to thank her cordially for the idea to translate the German text as well as for her energy and faith to realize this project herself, regardless of her advanced age. May she continue her work in the history and philosophy of science for a long time still, and may other authors profit from her scholarship as I did!

Thanks also go to my editor at the University of Rochester Press, Timothy J. Madigan, for his spontaneous acceptance of this project and his continuous support during its realization. I wish to share my pleasure in the publication of this book with all who have contributed to it in any way.