Although the causative organism of lobar pneumonia is definitely known, much remains to be learned regarding the mode of infection and the nature of the disease. With the discovery of pneumococci in the mouths of normal individuals, the belief became prevalent that pneumonia was an autogenous infection depending on a change of virulence of these mouth pneumococci, or a decrease in resistance on the part of the host. Proof of this theory is lacking, however, and evidence now at hand indicates that the strains of pneumococci causing the infection in 80 per cent. of cases differ inherently from those inhabiting the mouth under normal conditions. Furthermore, it seems probable that pneumonia is a contagious disease and is acquired by contact with patients suffering from the disease, or with true pneumonia carriers.
Recent investigation1 along lines suggested by Neufeld indicates that the pneumococci from cases of lobar pneumonia may be