Abstract
This study forms a part of a general investigation by the Bureau of Laboratories and the Influenza Commission of the Metropolitan Life Insurance Company of the flora of the respiratory tract in normal and pathological conditions. The purpose of this section of the work was to determine whether any one variety of pneumococcus would be encountered more frequently in epidemic inflammatory conditions resembling influenza than in those of the nature of ordinary colds and in the normal controls. If, in a wave of common colds or influenzal-like inflammations, a dominant variety could be demonstrated in the majority of cases it would suggest strongly that the pneumococcus strain in question was the primary causative agent of the outbreak in which it was prevalent. The presence of a single type of a pathogenic variety in the individual case may indicate, however, that it is either the primary agent or one of the secondary invading bacteria; or that it may be only an accidental parasitic variety.
