PATHOGENICITY FOR MAN 215 



ance in the host. The organisms may be virulent or avirulent and 

 they may sometimes be found as the predominant bacterial species 

 but, contrary to the older opinion, these so-called normal pneumo- 

 cocci, although possessed of full virulence, rarely cause pneumonia 

 in the individual in whom they temporarily dwell. Since the dis- 

 covery by Sternberg, 1316 " 8 Pasteur, 1065 " 6 and other early investiga- 

 tors that pneumococci virulent for laboratory animals were to be 

 found in the saliva of healthy persons, many reports have ap- 

 peared concerning the frequency of the occurrence. Buerger 

 (1905), 164 by the plate method, detected pneumococci in the 

 mouths of thirty-nine out of seventy-eight normal persons. Some of 

 the subjects were assumed to have acquired the organisms in hos- 

 pital wards and others as a result of pneumonia. In both groups, 

 the pneumococci persisted for days and even months. In a com- 

 munication published at the same time, Hiss, Borden, and Knapp, 651 

 from their bacteriological study of twenty-two healthy individuals, 

 concluded that practically every person, at least during the win- 

 ter season, living under such conditions as exist in New York City, 

 acts as a host at some time or other and probably at repeated in- 

 tervals for Pneumococcus. A seasonal effect on the distribution of 

 pneumococci was suggested by Longcope and Fox 825 who observed 

 a greater incidence of the organism in normal human beings during 

 the winter months than during the milder seasons. The authors 

 stated that during the winter a large percentage of healthy indi- 

 viduals harbor virulent pneumococci in the buccal cavity, and that 

 it is almost certain that some persons always have virulent pneu- 

 mococci in their saliva. More recently, Brown and Anderson 

 (1932) 152 noted a correlation between the incidence of pneumo- 

 cocci in the throats of normal persons and periods of inclement 

 weather. 



Park and Williams, 1058 by the mouse inoculation method, found 

 pneumococci in the sputum of 55 per cent of over two hundred 

 healthy subjects. McLeod, 880 in reviewing these reports, gave the 



