The article by Fred. Griffith, a Medical Officer of the Ministry of Health, explores the significance of pneumococcal types in lobar pneumonia. The study is based on observations from 150 cases of lobar pneumonia between April 1920 and January 1922, with additional data collected from January 1922 to March 1927. The main finding is the progressive decrease in cases attributed to Type II pneumococcus, suggesting a possible increase in Group IV cases. However, the isolation of Group IV strains from sputum does not prove causality, as different serological types can coexist in the same patient. Griffith describes several instances where multiple serological types of pneumococci were found in the sputum of pneumonia patients, raising questions about the origin and evolution of these strains. He presents detailed experiments to investigate the transformation of pneumococci, including the production of attenuated strains through growth in immune serum and solid media. The article also discusses the reversion of attenuated rough strains to virulent smooth strains, and the conditions under which this reversion occurs, such as the size and concentration of the bacterial mass inoculated into the mouse. The findings suggest that the transformation of pneumococci may be influenced by the presence of protective antibodies and the availability of soluble substances that stimulate or nourish the bacteria. The article concludes with a discussion on the implications of these observations for understanding the dynamics of pneumococcal infections and the potential for developing vaccines or treatments.The article by Fred. Griffith, a Medical Officer of the Ministry of Health, explores the significance of pneumococcal types in lobar pneumonia. The study is based on observations from 150 cases of lobar pneumonia between April 1920 and January 1922, with additional data collected from January 1922 to March 1927. The main finding is the progressive decrease in cases attributed to Type II pneumococcus, suggesting a possible increase in Group IV cases. However, the isolation of Group IV strains from sputum does not prove causality, as different serological types can coexist in the same patient. Griffith describes several instances where multiple serological types of pneumococci were found in the sputum of pneumonia patients, raising questions about the origin and evolution of these strains. He presents detailed experiments to investigate the transformation of pneumococci, including the production of attenuated strains through growth in immune serum and solid media. The article also discusses the reversion of attenuated rough strains to virulent smooth strains, and the conditions under which this reversion occurs, such as the size and concentration of the bacterial mass inoculated into the mouse. The findings suggest that the transformation of pneumococci may be influenced by the presence of protective antibodies and the availability of soluble substances that stimulate or nourish the bacteria. The article concludes with a discussion on the implications of these observations for understanding the dynamics of pneumococcal infections and the potential for developing vaccines or treatments.