3fH. PATHOGENIC MICROORGANISMS 



reasons mentioned in another place, the streptococcus (seu pneumococ- 

 eus) niucosus. Both the methods of protection and agglutination per- 

 mitted such a grouping. Groups I and II are made up of organisms 

 that are respectively identical, since the members of each group react, 

 in protection and the agglutination experiments, with sera produced 

 by individuals of the same group. Group III is distinctive and repre- 

 sents the pneumococcus mucosus, but immune reactions with members 

 of this group are very difficult. Group IV is a heterogeneous collection 

 of organisms which have no distinctive characteristics, and each individ- 

 ual member seems serologically isolated. Thus, the only groups in 

 which exact serological experiments can be made are those now classi- 

 fied as I and II. 1 



In 223 cases of lobar pneumonia Dochez finds the various types dis- 

 tributed as follows: 



Types of Number Per 



Pneumococci of Cases Cent. 



I 78 34.97 



II 75 33.63 



III 22 9.86 



IV 48 21.52 . 



Total number of cases 223 



Groups I, II and III seem to be most frequently associated with dis- 

 ease, whereas members of Group IV are often found in the mouths of 

 normal people. Groups I, II and III, moreover, are found in the 

 sputum of normal individuals rarely except in association with the dis- 

 ease, but often in individuals who have been closely associated with 

 cases of pneumonia and in convalescents. Dochez and Avery 2 accord- 

 ingly suggest the possibility of pneumonia carriers and also come to the 

 conclusion that pneumonia is rarely an autogenous infection of the lungs 

 with the organism harbored for a long time in the mouth, but is as a 

 rule an infection with a virulent strain of pneumococcus from without, 

 carriers furnishing an important element in the transmission from pa- 

 tients to the healthy. Such contagiousness is also suggested by the 

 apparent epidemics at Panama and in Africa, mentioned in a preceding 

 paragraph. 



Precipitins have been demonstrated in pneumococcus immune serum 



1 Recently Miss Olmstead, in our laboratory, has obtained results which promise 

 the eventual subdivision of Group IV into definite divisions. 



2 Dochez and Avery, Jour, of Exper. Med., 1915, xxi, 114. 



