PNEUMOCOCCUS TYPES AND TYPING 413 



pneumococci are of less importance than those of the other 

 groups. They are associated with about one-fifth of all 

 pneumonias and cause only about 7 per cent, of fatalities. 



Further, when by appropriate methods of procedure 

 animals have been immunized from these groups, the blood 

 serum of such immune animals are found to have a favor- 

 able action in preventing infection in normal animals, but 

 here too there is a specific relationship, for the serum of 

 animals immune from either Type I, II or III is impotent 

 when employed against infection by pneumococci of the 

 types not used for immunization. This specific relation- 

 ship must always be borne in mind in efforts to produce 

 sera possessing either prophylactic or curative properties 

 for the disease pneumonia. 



By an interchange of result, methods and materials 

 between various laboratories especially identified with the 

 development of these ideas, it has become possible to stand- 

 ardize the "typing" of pneumococci in a very satisfactory 

 manner. Specific antisera from animals highly immun- 

 ized from each type group of pneumococci are now avail- 

 able, and by the correct use of such sera in performing the 

 agglutination reaction, we may easily determine to which 

 type any pneumococcus in question belongs, as well as 

 form an approximate estimate as to the probable outcome 

 of the case of pneumonia from which that pneumococcus 

 was obtained. 



In consequence of all this we are obliged to modify our 

 views formerly held on the relation of pneumococci to 

 pneumonia. We are not any longer justified in believing 

 that the pneumococcus found in the normal mouth, under 

 conditions not known to us, changes from a harmless com- 

 mensal to a dangerous pathogenic species. All modern 



