ALL OF THOSE readers who were rendered nervous by Richard Preston's bestseller, The Hot Zone, may find comfort in the following account of a century of increasingly successful efforts to develop vaccine and serum antitoxin defenses against infection. They will be comforted, we believe, but not entirely relieved of concern. The search continues. Viruses and bacteria continue to emerge and evolve, posing new threats to human life and health. The quest for preventive medicines has a history with chapters but no conclusion. As long as there is human life, we will need institutions that will sustain the search for innovative means of fighting infection.

In Networks of Innovation, our emphasis is on the private sector's contribution to the process of innovation in vaccines and antitoxins. But as our title indicates, we placed the activities of the H. K. Mulford Company, Sharp & Dohme, and Merck & Co., Inc., in their historical context – a context that identifies the complex, loosely integrated institutional and personal networks that fostered innovation in this industry. The first of the networks that we examine took shape in the late nineteenth century around the central ideas of the bacteriological revolution. Other networks with distinctive leaders, values, scientific findings, and organizations followed during the twentieth century. Many of the relevant institutions in these networks were nonprofit professional organizations; many of the leaders were scientists in universities and research organizations. There were, as well, public institutions, including a rich array of public health organizations at the local, state, and federal levels in the United States. Other institutions in these networks were international in scope.