The mortality from pneumonia in childhood has always been greatest in infancy. In the infant ward at Cook County Hospital many patients with pneumonia are treated, and the mortality has always been high. In 1937 and 1938, before chemotherapy was used, the mortality rates were 32 per cent and 31 per cent respectively. The infants, all under 1 year of age, were drawn from essentially the same group and were treated by the same medical personnel and with the same therapeutic measures other than specific chemotherapy as the 1940 series which is the subject of this paper. While it is true that the incidence and mortality of pneumonia vary somewhat from season to season, these figures at least serve as a base line from which some conclusions can be drawn with regard to a human experiment in which adequate control is practically impossible.
With the advent of specific therapy, particularly