PATHOGENICITY FOR MAN 221 



geneous group may account for approximately 50 per cent of the 

 cases. Streptococci of both hemolytic and non-hemolytic varieties 

 have been found in about 31 per cent of the patients studied ; the 

 Pfeiffer bacillus and pneumococci of Types I and II were respon- 

 sible for 3.3 per cent each ; while Type III pneumococci appeared 

 two and one-half times as often as did strains of either Type I 

 or II. 



PNEUMOCOCCAL TYPES IN PNEUMONIA IN INFANTS AND 

 CHILDREN 



The data presented in Heffron's analyses make it appear that, 

 as far as reported, of pneumonia in children under twelve years of 

 age, 9 or 10 per cent of the cases were caused by Type I pneumo- 

 cocci, between 2 and 4s per cent were due to organisms of Type II 

 or III, while in approximately 75 per cent of the cases pneumo- 

 cocci of the remaining types appeared to be the causative organ- 

 isms. Heffron placed Types I, XIV, VI, V, and VII as the order in 

 which pneumococci are found in the pneumonias of childhood. 

 There appears to be a conspicuous rise in the frequency of pneu- 

 mococci of the first three types in pneumococcal pneumonia as age 

 increases. Dividing the children studied into one group comprising 

 those under three years of age and a second group in which the 

 ages ranged from three to twelve years, the most marked increase 

 is to be noted in the case of Type I Pneumococcus, which rose from 

 4.2 per cent in the first group to 20.2 per cent in the second. For 

 pneumococci of Types I, II, and III the corresponding combined 

 incidence was 11.1 and 25.2 per cent respectively in the two age 

 groups. The number of cases examined is too small to allow of ac- 

 curate statistical deduction, but the trend is significant and points 

 to the greater frequency of organisms of the first three serological 

 types in the higher age groups. 



Without burdening the text with too many tables, Heffron's 

 summary may be abridged to read : Among the 826 cases of pneu- 

 mococcal lobar pneumonia in children of eleven years of age or 



