PNEUMOCOCCUS, VARIETIES AND VARIATIONS 411 



These highly pathogenic types of pneumococcus are 

 rarely found in the normal mouth, except in case of persons 

 in close contact with cases of pneumonia; and of equal 

 importance is the fact that under such circumstances the 

 pneumococcus found in the mouth of the normal individual 

 ("the contact") is identical to that found in the discharges 

 from the lungs of the particular patient suffering from 

 pneumonia with whom he has been in contact. Such 

 virulent pneumococci ultimately disappear from the air 

 passages of the convalescent from pneumonia, as well as 

 from the mouth of the healthy contact. 



If one secure from the normal air passages the pneumo- 

 coccus commonly found there and at the same time secure a 

 culture of pneumococcus from a case of typical lobar pneumo- 

 nia, it will be found that in morphology and other biological 

 peculiarities the two cultures are, as a rule, indistinguishable 

 the one from the other. On the other hand, if animals be 

 immunized from each culture it will be found that the blood 

 serum of each of the immune animals agglutinates only its 

 homologous cultures; that is to say, the serum of the animal 

 immunized by the use of pneumococcus from the case of 

 pneumonia agglutinates the pneumococcus from only that 

 case and similar cases, but not the pneumococcus common 

 to the normal mouth or pharynx. While the serum from the 

 other animal agglutinates only the pneumococcus used in 

 the immunization of that animal. In other words, we have 

 specific agglutinations. 



If we examine in the same manner all cases of pneumonia 

 we find pneumococci differing specifically in their agglu- 

 tinating reactions not only from those frequent in the 

 normal mouth, but with various manifestations of the 

 disease we find variations in the virulent pneumococci 

 specifically related to them. 



