218 ACUTE PNEUMONIA. 



in the more susceptible representatives of the lower 

 animals. 



A fact which has, in the minds of some, rather mili- 

 tated against the pneumococcus being the cause of pneu- 

 monia is the discovery of this organism in the saliva of 

 healthy men. This fact was early pointed out by Pasteur, 

 and also by Fraenkel, and the observation has been con- 

 firmed by many other observers. It can certainly be isolated 

 from the mouths of a considerable proportion of normal 

 men, from their nasal cavities, etc., being probably in any 

 particular individual more numerous at some times than at 

 others, and sometimes being entirely absent. This can be 

 proved, of course, by inoculation of susceptible animals. 

 Such a fact, however, does not necessarily imply that the 

 pneumococcus is not the cause of pneumonia. It only im- 

 plies the importance of predisposing causes in the etiology 

 of the disease, and it is further to be observed that we have 

 corresponding facts in the case of the diseases caused by 

 pyogenic staphylococci, streptococci, the bacillus coli, etc. 

 It is probable that by various causes the vitality and power 

 of resistance of the lung are diminished, and that then the 

 pneumococcus gains an entrance. In relation to this possi- 

 bility we have the very striking facts that in the irregular 

 forms of pneumonia, secondary to such conditions as typhoid 

 and diphtheria, the pneumococcus is very frequently present, 

 alone or with other organisms. Apparently the toxines 

 produced by such bacteria as the B. typhosus and the 

 B. diphtheriae can devitalise the lung to such an extent that 

 secondary infection by the pneumococcus is more likely to 

 occur and set up pneumonia. We can therefore understand 

 how much less definite devitalising agents such as cold, 

 alcoholic excess, etc., can play an important part in the 

 causation of pneumonia. In this way also other abnormal 

 conditions of the respiratory tract, a slight bronchitis, etc., 

 may play a similar part. 



It is more difficult to explain why sometimes the pneumo- 

 coccus is associated with a spreading inflammation, as in 

 croupous pneumonia, whilst at other times it is localised 



