Specificity 



473 



croupous pneumonia. Netter* found it 82 times in 82 autopsies 

 upon such cases; Kleiliperer, 21 times out of 21 cases studied by 

 puncturing the lung with a hypodermic syringe. Weichselbaum ob- 

 tained it in 94 out of 129 cases; Wolf, in 66 out of 70; and Pierce, 

 in no out of 121 cases. In about 5 per cent, of the cases it remains 

 localized in the respiratory apparatus; in 95 per cent., it invades the 

 blood. An interesting paper upon this subject has been written by 

 E. C. Rosenow.f 



The conditions under which it enters the lung to produce pneu- 

 monia are not known. It is probable that some systemic depravity 

 is necessary to establish susceptibihty, and in support of this view 

 we may point out that pneumonia 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 



Fig. 1 70. — Biplococcus pneumoniae. Colony twenty-four hours old upon 

 gelatin. X 100 (Frankel and PfeifFer). 



form of vital depression is necessary to predispose to the disease, 

 further study will be required to tell. 



Vinilence.^Pneumococci vary greatly in virulence, and rapidly 

 lose this quaUty in artificial culture. When it is desired to maintain 

 or increase the virulence, a culture must be frequently passed through 

 animals. Washbourn found, however, that a pneumococcus isolated 

 from pneumonic sputum and passed through one mouse and nin6 

 rabbits developed a permanent virulence when kept on agar-agar 

 so made that it was not heated beyond ioo°C., and alkahnized 4 cc. 

 of normal caustic soda solution to each hter beyond the neutral point 

 determined with rosolic acid. The agar-agar is first streaked with 

 sterile rabbit's blood, then inoculated. The cultures are kept at 



* " Compte-rendu," 1889. 



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



