200 ACUTE PNEUMONIA. 



as the B. typhosus and the B. diphtheriae can devitalise the 

 lung to such an extent that secondary infection by the pneu- 

 mococcus is more likely to occur and set up pneumonia. 

 We can therefore understand how less definite devitalising 

 agents such as cold, alcoholic excess, etc., can play an im- 

 portant 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 pneu- 

 mococcus is associated with a spreading inflammation, as 

 in croupous pneumonia, whilst at other times it is present 

 in the catarrhal bronchioles and air vesicles in broncho- 

 pneumonia. It is quite likely that in the former condition 

 the organism is possessed of a higher order of virulence, 

 though of this we have no direct proof. We have, however, 

 a closely analogous fact in the case of erysipelas, which, 

 we have stated reasons for believing, is produced by a 

 streptococcus which, when less virulent, causes only local 

 inflammatory and suppurative conditions. 



Summary. We may accordingly summarise the facts 

 regarding the relation of Fraenkel s pneumococcus to the 

 disease by saying that it can be isolated from nearly all 

 cases of acute croupous pneumonia, and also from a con- 

 siderable proportion of other forms of pneumonia. When 

 injected into the lungs of moderately insusceptible animals 

 it gives rise to pneumonia. If, in default of the crucial 

 experiment of mtra-pulmonary injection in the human 

 subject, we take into account the facts we have discussed, 

 we are justified in holding that it is the chief factor in 

 causing croupous pneumonia, and also plays an important 

 part in other forms. Pneumonia, in the widest sense of 

 the term, is, however, not a specific affection, and various 

 inflammatory conditions in the lungs can be set up by the 

 different pyogenic organisms, by the bacilli of diphtheria, 

 of influenza, etc. 



The possibility of Friedlander's pneumobacillus having 

 an etiological relationship to pneumonia has been much 

 disputed. Its discoverer found that it was pathogenic 



