CLASSIFICATION OF PNEUMOCOCCI 109 



Types I, II, and III and then divided the members of Group IV 

 into at least twelve groups, some of which contained subgroups. In 

 a subsequent report, Olmstead 1028 suggested that some members of 

 these groups served as connecting links between Type II and 

 Group IV, and, because of a closer relationship with the latter, 

 should be classed as Pneumococcus IV rather than as IIX. The 

 same proposal was made by Clough, 238 who after identifying 

 strains of Avery's subgroups IIA and IIB among 121 cultures 

 isolated from cases of lobar pneumonia, suggested that, since mem- 

 bers of these two subgroups possessed relatively low virulence for 

 animals and had been recovered from the mouths of normal per- 

 sons, the strains would be found epidemiologically to resemble 

 Group IV organisms more closely than those of Types I or II. 



Nicolle, Jouan, and Debains 1011 did not accept Group IV and the 

 American classification, claiming that a large number of pneumo- 

 cocci studied by them were not agglutinated by their own or 

 American serums, except when treated with dilute hydrochloric 

 acid according to the method of Porges. The authors recommended 

 that the conception of Type IV — a purely negative type — ought 

 then to be abandoned henceforth. 



Nicolle with Debains 1009 again studied by the agglutination re- 

 action a large number of pneumococci from varied sources. They 

 used the American classification and their results showed that the 

 strains, as studied, varied in agglutinability from a complete ab- 

 sence of this property to spontaneous clumping in normal horse 

 serum. 



In a review of various immunological reactions, Nicolle and De- 

 bains (1920) 1010 concluded that races of Pneumococcus — "anti- 

 genic races" — could not be determined by agglutination alone. 

 Their work is, in one respect, reminiscent of Gillespie's 516 data on 

 the acid agglutination of pneumococci. Tested by this method, 

 strains belonging to Types I and II had, as a rule, narrow zones 

 of agglutination. Other pneumococci had broad zones, or in a few 

 cases, narrow zones not coincident with those occupied by organ- 



