In the early twentieth century, public health officers were responsible for the identification and control of infectious diseases, monitoring the sanitary status of towns and cities, and preventing the spread of contagious diseases. Early public health reformers were concerned with the environment—particularly miasmas carrying noxious chemicals assumed to be polluting the air, water, and soil. The work of Louis Pasteur, Robert Koch, and other microbiologists shifted attention from disease-causing miasmas to the microbes that caused infectious epidemic diseases. When the Centers for Diseases Control and Prevention reviewed public health achievements from 1900 to 1999, improvements in the health of mothers and babies were cited as particularly commendable. The history of public health as a key component of the history of medicine should logically proceed from ancient warnings about miasmatic swamp air to a scientifically based system of protecting human health from polluted air and unsafe water, but all too often history actually reveals an increasing burden of environmental hazards.