BACILLUS PNEUMONLE. 259 



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with regard to their growth in gelatine and with regard 

 to the species of animals susceptible to their action, and 

 these differences enable us to distinguish them from 

 Friedlander's bacilli. But the diagnosis of the latter 

 can only be made by the aid of elaborate comparative 

 cultivations and experiments on animals. And hence 

 the establishment of a causal connection of these bacilli 

 with pneumonia, based on their distribution in pneumonic 

 processes, is very difficult, because it is not possible in 

 every case to employ all the methods which alone enable 

 us to distinguish these organisms from others which are 

 constantly present in the sputum and in the bronchi, 

 and which are therefore frequently found in pneumonic 

 exudation, although they are of no importance. 



The answer to these questions is so much the more 

 difficult because Friedlander's bacilli are, without doubt, 

 not the only cause of the pneumonic process. We are 

 already acquainted with pneumonias which are caused 

 by aspergillus and actinomyces ; it is a priori not im- 

 probable that also among bacteria there are several other 

 species which can set up pneumonia ; and the probability 

 of this view is increased by Schou's observations. Further 

 careful observations, combined with cultivations and ex- 

 periments on animals, will therefore possibly discover a 

 greater variety of causes of pneumonia.* 



Emmerich has demonstrated the presence of Fried- Occurrence of 

 lander's bacilli in the soil of a room in which there were ba 

 many pneumonic patients ; the diagnosis was rendered the human 

 certain by inhalation experiments with cultivations on 

 18 mice, of which 8 died of pneumonia ; hence the soil 

 seems to be one of the places where the pneumonia 

 bacilli can be preserved, and whence, in suitable cases, 

 they may pass into human beings. Possibly also there 

 are a number of other places in our surroundings which 

 play a similar r6le. But as the result of our present 

 knowledge as to their occurrence and their properties, 

 we cannot make any more definite statement with regard 

 to the mode of spread of these pneumonia bacilli. 



* Friinkel has isolated a bacillus which is much more often associated 

 with pneumonia than the above-mentioned organism. 



