Pathogenesis 



337 



according to the postulates of Koch. The invariability of 

 its presence in croupous pneumonia is, however, very con- 

 vincing, as Netter * found it 82 times in 82 autopsies upon 

 such cases ; Klemperer, 2 1 times out of 2 1 cases studied by 

 puncturing the lung with a hypodermic syringe. Weichsel- 

 baum obtained it in 94 out of 129 cases; Wolf, in 66 out of 

 70 ; and Pierce, in 1 10 out of 12 1 cases. In about 5 per cent, 

 of the cases it remains localized in the respiratory apparatus ; 



Fig. 101. Diplococcus pneumonias. Colony twenty-four hours old 

 upon gelatin. X 100 (Frankel and Pfeiffer). 



in 95 per cent, it invades the blood. An interesting paper 

 upon this subject has been written by B. C. Rosenow.f 



The conditions under which it enters the lung to produce 

 pneumonia are not known. It is probable that some 

 systemic depravity is necessary to establish susceptibility, 

 and in support of this view we may point out that pneu- 

 monia is very frequent, and exceptionally severe and fatal, 

 among drunkards, and that it is the most frequent cause of 

 death among the aged. Whether, however, any particular 

 form of vital depression is necessary to predispose to the 

 disease, further study will be required to tell. 



* " Compte-rendu," 1889. 

 f'Jour. Infectious Diseases," 1904, i, p. 280. 

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