222 BIOLOGY OF PNEUMOCOCCUS 



under, Type I organisms were found in 22.4 per cent, Type II in 

 8.1 per cent, and Type III in 5.5 per cent, these three types to- 

 gether accounting for 36.0 per cent of the infections. Sixty-four 

 per cent of the remaining cases were due to pneumococci of the 

 other serological types. Of all the various types, XIV, I, VI, V, 

 and VII were the more prevalent, with IV, IX, XV, and XIX of 

 frequent occurrence. 



In pneumonias of the bronchial type the picture is somewhat 

 different. Whereas Type II Pneumococcus showed slightly greater 

 frequency, Type I organisms fell in percentage of occurrence from 

 22.4 to 9.0, and Types I, II, and III combined showed a decrease 

 of from 36.0 to 26.2 per cent. The respective rates for pneumo- 

 cocci other than those of the first three types were reported to be 

 substantially the same for infants and children and for adults. 



To recapitulate the enumeration so far reported of the com- 

 monest serological types of Pneumococcus in order of approximate 

 frequency as occurring in infants, children, and adults, the follow- 

 ing figures from Heffron are presented: 



Lobar pneumonia 



Infants and children . . . . XIV, I, VI, V, VII 



Adults I, II, III, VIII, VII, V 



Bronchopneumonia 



Infants and children .... VI, XIX, XVIII 



Adults Ill, VIII, XVIII, X, V, VII 



Serological Types and Fatality-Rates 



The factors making for virulence of pneumococci have been dis- 

 cussed in Chapter VI. In addition to the characters of individual 

 strains dependent upon their history and immediate environment, 

 there are variations in invasive power peculiar to the many sero- 

 logical types. The data so far accumulated on the fatality-rates 

 of the different types are not extensive but enough evidence is at 

 hand to warrant some general, if tentative, conclusions. Heffron 

 stated that from available reports the fatality-rates, at least for 



