100 THE STORY Of THE BACTERIA. 



actual causes, while exceedingly important, are 

 yet simply predisposing factors. They believe 

 that the reason why pneumonia is so frequently 

 associated with these conditions is that they 

 in some way fit the lungs to be a good grow- 

 ing place for the germs if at the favorable 

 moment they gain access to them through the 

 mouth. 



We do not know much about the bacteria 

 which thus appear to cause pneumonia, so far 

 as their lurking places outside of the body are 

 concerned. But they are not infrequently 

 found in the mouths of healthy persons, and 

 are most likely distributed through the air with 

 the dust. 



The pneumonia which so frequently comes 

 on as a serious complication of diphtheria has 

 been shown to be caused by the germs which 

 cause the diphtheria itself getting down into 

 the lungs and producing their poisonous effects 

 there. 



Scarlet-Fever, Measles, Yellow-Fever, etc. 

 There is a great deal in the nature and mode 

 of communication of scarlet-fever, measles, 



