PNEUMOCOCCUS INFECTION 209 



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 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 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 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 there- 

 fore 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 septicaemic complications of 

 pneumonia, such as empyema and meningitis, render it possible 

 that it may be the causal agent in a few cases of the disease. 



In the septic pneumonias the different pyogenic organisms 

 already described are found, and sometimes in ordinary 

 pneumonias, especially the catarrhal forms, other organisms, 

 such as the b. coli or its allies, may be the causal agents. 



The Pathology of Pneumococcus Infection. The effects of 

 the action of the pneumococcus, at any rate in a relatively 

 insusceptible animal such as man, seem to indicate that toxins 

 must play an important part. Pneumonia is a disease which 

 presents in many respects the characters of an acute poisoning. 

 In very few cases does death take place from the functions of 

 the lungs being interfered with to such an extent as to cause 

 asphyxia. It is from cardiac failure, from grave interference 

 with the heat-regulating mechanism, and from general nervous 

 depression that death usually results. These considerations, 

 taken in connection with the fact that in man the organisms are 

 found in the greatest numbers in the lung, suggest that a toxic 

 action is at work. Various attempts have been made to isolate 

 toxins from cultures of the pneumococcus, e.g. by precipitating 

 14 



