ETIOLOGICAL RELATIONS TO PNEUMONIA. 199 



ducer of general septicaemia in animals, we have seen, finds 

 a perfectly rational explanation in the different degrees 

 of susceptibility which exist towards it in different species. 

 In this connection the occurrence of manifestations of 

 general infection associated with pneumonia in man is 

 of the highest importance. We have seen that menin- 

 gitis and other inflammations are not very rare complica- 

 tions of the disease, and such cases form a link connecting 

 the local disease in the human subject with the general 

 septicasmic processes which may be produced artificially 

 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 

 confirmed by many other observers. It can certainly be 

 isolated from the mouths of a large 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 pneu- 

 mococcus is not the cause of pneumonia. It only implies 

 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. Taking this in conjunction 

 with the fact that the pneumococcus can by itself originate 

 such conditions in susceptible animals, we are justified in 

 the conclusion that the toxines produced by such bacteria 



