The classification of cases of pneumonia according to their bacterial etiology has proved of considerable value to our understanding of the disease. The majority of the cases are due to the pneumococcus, and a small minority are due to other pyogenic organisms. The division of the pneumococci into types has brought out the importance of types I, II and III and has made possible the development of specific therapeutic antiserums for types I and II.
A large number of strains that had not been serologically identified were formerly classified together for convenience as type or group IV.1 They were known to occur in a great variety of pneumonias and other pneumococcic infections2 but could also be recovered from the throats of about 50 per cent of normal persons on one examination, and from the throats of all on repeated examinations.3 It remained for Cooper4 to isolate
SUTLIFF WD, FINLAND M. THE SIGNIFICANCE OF THE NEWLY CLASSIFIED TYPES OF PNEUMOCOCCI IN DISEASETYPES IV TO XX INCLUSIVE. JAMA. 1933;101(17):1289–1295. doi:10.1001/jama.1933.02740420009003