TEXT-BOOK OF BACTERIOLOGY. 305 



Let us be guided by Koch's demands that a specific kind of bac- 

 terium is to be found in all cases of the disease, and in it alone, 

 and microscopical investigation having proved this, succcessful 

 culture must confirm and transmission ultimately settle it. 



It is a generally-admitted fact that the pneumococci cannot be 

 observed in all cases of croupous lung inflammation, and the num- 

 ber of positive results is considerabty less than that of the negative 

 ones. Nor is the exclusive occurrence of Friedlander's cocci in 

 pneumonia asserted anywhere, many communications having 

 taught us that the same, or very similar, bacteria appear in the 

 saliva and nasal secretions of healthy persons and in the pulmon- 

 ary expectorations of persons affected with other diseases. 



The claims of the pneumococci are, therefore, hardly to be sus- 

 tained. Their value as a cause of pneumonia is the more doubtful 

 because the way in which Friedlander discovered them was not 

 exactly free from objection. He did not use the plate method, but 

 brought pieces of the lung-tissue, pulmonary fluid, etc., imme- 

 diately on solid gelatin, thus committing the same mistake, the 

 fatal consequences of which were evident with Emmerich's Neapoli- 

 tan bacilli. 



Neither microscopic investigation nor culture nor transmission 

 having furnished sufficient proofs for the assertion that the pneu- 

 mococci play a decided role in the origin of pneumonia, \ve cannot 

 recognize them as the causal factors of this disease. But it should 

 not be overlooked that Friedlander's bacteria have been unobjec- 

 tionably obtained in inflammation of the lungs by numerous relia- 

 ble investigations. It may, therefore, be assumed that they are 

 at any rate related to the said affection, and it may not be amiss to 

 regard them (like the streptococci in typhoid) as subsequent settlers. 

 on a soil prepared and properly fitted by the activity of some other 

 micro-organisms. 



XVI. PNEUMOCOCCUS (A. FRAENKEL). 



We are sustained in the opinion just expressed by the fact that 

 we already know a species of bacteria radically different from Fried - 

 lander's, and, as it seems, taking an exclusive or decisive part in 

 causing pneumonia. 



A. Fraenkel observed in the sputum of persons afflicted with 

 lung disease, especially in the rusty sputum of pneumonia, a peculiar 

 micro-organism which proved to be pathogenic for several species of 

 animals, and was called by its discoverer " the microbe of sputum 

 septicaemia." Fraenkel asserted later, on the basis of minute in- 

 vestigations, that " it was to be regarded as the usual exciter of 

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