The rise of modern science, especially modern biological science, has been tied to a close observation of nature. This is most closely associated with the brilliant observations of Andreas Vesalius whose anatomical drawings are as much works of art as they are careful delineations of the human form. Yet, if we have learned anything from the revolution in history and philosophy of science of the 1960's and 70's, we have learned that "observation" is "theory-laden." To a very large extent, what we see is predetermined by the theory to which we ascribe. In anatomy and physiology, this "fact" can be seen in the observations of the human body. For centuries, for example, writers on anatomy and physiology wrote of the "horns" of the uterus and a five-lobbed liver; but it is "apparent" to us that the human uterus has no "horns" while the liver has only two lobes, not five. Similar observational "errors" can be found in dealing with the heart--we now believe that the blood "circulates" but for millennia, the arterial and venal systems were considered to be separate. Because the relationship of theory with observation is central to contemporary philosophy of science, it is important to understand their relationship in this first great modern observer of the human anatomy. Andreas Vesalius's De humani corporis fabrica, first published in 1543, is generally acknowledged to be one of the most important books of the Renaissance. Yet Vesalian scholarship has mostly been concentrated on the illustrations, his minor works, and his biography. The lengthy text of the Fabrica--that is, the part of the work that presents the theory which controlled in some sense what he observed--has been much less studied. With this grant, Professor Siraisi aims to elucidate Vesalius's understanding and presentation of anatomy and physiology in his principal work in the context of the scientific culture of the age. Her objective is to investigate the Fabrica as an example of Renaissance scientific writing, considering text and illustrations together as Vesalius intended his readers to do. The result will be a close reading of the scientific and scholarly activities involved in Renaissance anatomy and their relationship to humanistic medical culture, as well as a fuller picture of the scientific and cultural assumptions of a leading figure in Renaissance science. The study will address several broad historical themes of current interest: the role of the life sciences in scientific developments of the 16th and 17th centuries; 16th century humanistic medical learning and the culture of the medical community; the development of early modern scientific methodology and values, including the role of physical demonstration and methods of persuasion and proof. Her results will be of interest to philosophers of science, especially of biology, of historians of science and medicine, and Renaissance cultural and intellectual historians.