For at least 40 years there has been a great interest in the problems created by infectious airborne agents and other toxic sub stances transported through the air. During the Second World War, this problem grew out of the very high incidence of upper respira tory infections appearing in new military recruits who were brought together in very large, open quarters. As a result, very interest ing methods were developed to measure these airborne agents, espe cially bacteria, and some important methods were refined for their control. These methods primarily concentrated on ultraviolet radia tion,...