PATHOGENICITY FOR MAN 233 



mococci of Group IV accounted for 75 per cent of the positive 

 cultures. 



The studies reported by Rosenau, Felton, and Atwater, 1157 and 

 by Powell, Atwater, and Felton 1106 in 1926 yielded results which, 

 while differing in some respects from those of Dochez and Avery, 

 confirm their thesis and throw additional light on the carrier prob- 

 lem. Using a thoroughgoing technique for the isolation of pneumo- 

 cocci from the mouth and throat, the Boston authors isolated 

 pneumococci of Type I from four times as many subjects in con- 

 tact with cases of lobar pneumonia as normal persons not thus ex- 

 posed. Type III organisms were recovered in twice as many in- 

 stances for every one hundred cases in the first group as in the 

 second, but there was no appreciable difference in the incidence of 

 Type II pneumococci. Strains belonging to Group IV occurred in 

 83.5 per cent of the former and in 69.3 per cent of the latter sub- 

 jects. The differences in the percentages representing the incidence 

 of pneumococci of the first three types, as reported by the Boston 

 and by the New York observers, may have been due to the broader 

 inclusion by the Boston workers of persons in the near neighbor- 

 hood of pneumonia patients. 



The rarity of pneumococci of Types I, II, and III in persons far 

 removed from centers in which pneumonia is endemic has been re- 

 ported by Milam and Smillie (1931). 903 In the isolated tropical 

 island, St. John, of the United States Virgin Islands, the pneumo- 

 cocci found in the nasopharyngeal flora of normal persons were 

 avirulent, and representatives of the first three types were seldom 

 present. Even city dwellers in a colder climate may enjoy com- 

 parative freedom from the more common disease-producing types 

 of pneumococci. In an extended investigation, embracing monthly 

 examinations over a period from two months to three and one-half 

 years, of 105 children and adults living in New York City, Web- 

 ster and Hughes (1931 ) 1495 obtained pneumococci at one time or 

 another from the nasal passages or the throat of 80 per cent of the 



