This Science and Society Dissertation Improvement Grant provides funding for a student to travel to archives to collect data and thereby assist in his completing his dissertation in the field of the history of science. The dissertation offers a historical explanation of the development of the research on aging in the first half of the twentieth century. It will investigate how the American scientists provided a new theory and methodology for studying senescence during the early twentieth century, and how the social turmoil in the Great Depression and the Second World War prompted them to institutionalize their research as a multidisciplinary field. The first part of the project deals with several biologists and biomedical scientists who contributed to transforming knowledge on aging, including Alexis Carrel, Alfred Cohn, Raymond Pearl, H. S. Jennings, and young Edmund Vincent Cowdry. Unlike previous historians who have argued that there was no essential change in the scientific understanding of aging during this period, the project will study how new experimental approaches to senescence brought about the idea that aging was only a contingent and local phenomenon. This idea considerably differed from the traditional thought that aging was an inevitable consequence of the decay or decrease of some vital principle governing the whole body. The second part of the dissertation will analyze how different social structures and responses to the economic problems in America and Britain during the Depression and the War conditioned the distinct forms of gerontology's development and institutionalization in the two countries. Particularly, the role of Vladimir Korenchevsky and the Nuffield Foundation in building gerontology in Britain will be compared with that of Edmund Cowdry, Clive M. McCay, and the Josiah Macy Jr. Foundation in the United States. The project will analyze how and why the latter was more successful in constructing larger multidisciplinary networks of the researchers of aging than the former, although it was the British scientists who initiated this movement and influenced the Americans. Finally, the project investigates the British scientist Peter B. Medawar's conception of the evolutionary theory of aging in 1946 and its reception in broader cultural and intellectual contexts, especially through contemporary Britons' increasing concerns about the aging of their population and the influence of new evolutionary theories. This project has two intellectual merits. First, it will explain how and why scientific ideas of aging underwent a substantial change during the early twentieth century, although it had not been greatly altered since the time of Aristotle and Galen. The dissertation investigates how scientific understanding of senescence began to be transformed through novel experimental approaches like tissue culture and genetic analysis within new institutional environments, especially those of the Marine Biological Laboratory at Woods Hole, the Rockefeller Institute of Medical Research, and several university biology departments. Second, the project will offer a comparative analysis on how distinct social conditions and their changes in America and Britain during the Great Depression and the Second World War brought about different forms of institutionalization of gerontology in these two countries. The broader impacts of the project upon the history and historiography of science are twofold. First, it will further our understanding of the nature of scientific discourse on the category of age, which has been much less studied than that of gender, race, and class. Second, it will analyze the nature of multidisciplinary investigation and the extent of its success in America and Britain during this period. This will reveal how and why scholars with distinct professional norms and assumptions, such as cytologists, biochemists, actuaries, psychologists, and anthropologists, decided to study aging from their diverse perspectives and to institutionalize their cooperative scientific approach.