218 INFLAMMATORY AND SUPPURATIVE CONDITIONS. 



other organisms. Apparently the effects produced by such 

 bacteria as the B. typhosus and the B. diphtherias can devitalize 

 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 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 to the catarrhal 

 patches in broncho-pneumonia. It is quite likely that in the 

 former condition the organism is possessed of a different 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 strepto- 

 coccus which, when less virulent, causes only local inflammatory 

 and suppurative conditions. 



Summary. We may accordingly summarise the facts re- 

 garding 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 considerable 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 intrapulmonary 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 con- 

 ditions 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 towards mice ancl 

 guinea-pigs, and to a less extent towards dogs. Rabbits appeared 

 to be immune. The type of the disease was of the nature of a 

 septicaemia. No extended experiments, such as those performed 

 by Gamaleia with Fraenkel's coccus, have been done, and there- 



