Well over one decade has passed since the appearance of the original four volumes of Membrane Transport in Biology. Since the publication of the last volume there have been spectacular advances in this field. These advances have been in part the result of the application of exciting new methodologies, and in part the result of new insights into the regulation and integration of transport processes. This volume, as well as a sixth volume, which is in preparation, are intended to cover key areas in which the development has been particularly striking. For many years the trend in studies of membrane transport had been that of increasing specialization with regard to the transporter of interest and of the cell or tissue studied. This trend was supported by the enormous number of publications directed at understanding the cellular physiology of specific organ systems and tissues, and also by the fact that different tissues often seemed to react so differently to the same conditions that mechanisms unique to each appear to be at play. One of the happy developments in recent years has been the realization that this apparent disparity of behaviors in different tissues is based on varying combinations of a limited number of transport mechanisms, all mediated by the same or similar proteins. Some of these transport proteins have already been isolated and analyzed with respect to amino acid sequence whereas others are just entering this phase.

Unevenly distributed resources and rising costs have become enduring problems in the American health care system. Health care is more expensive in the United States than in other wealthy nations, and access varies significantly across space and social classes. James A. Schafer Jr. shows that these problems are not inevitable features of modern medicine, but instead reflect the informal organization of health care in a free market system in which profit and demand, rather than social welfare and public health needs, direct the distribution and cost of crucial resources.
"The Business of Private Medical Practice" is a case study of how market forces influenced the office locations and career paths of doctors in one early twentieth-century city, Philadelphia, the birthplace of American medicine. Without financial incentives to locate in poor neighborhoods, Philadelphia doctors instead clustered in central business districts and wealthy suburbs. In order to differentiate their services in a competitive marketplace, they also began to limit their practices to particular specialties, thereby further restricting access to primary care. Such trends worsened with ongoing urbanization.
Illustrated with numerous maps of the Philadelphia neighborhoods he studies, Schafer's work helps underscore the role of economic self-interest in shaping the geography of private medical practice and the growth of medical specialization in the United States.