ETIOLOGICAL RELATIONS TO PNEUMONIA. 219 



to the catarrhal patches 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 intra- 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 

 towards mice and 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 therefore we cannot 

 say whether any similar pneumonic effects are produced by 

 it in partly susceptible animals. The organism appears to 

 be present alone in a small number of cases of pneumonia, 

 and the fact that it also appears to have been the only 

 organism present in certain septicfemic complications of 

 pneumonia, such as empyema and meningitis, render it 



