196 ACUTE PNEUMONIA. 



Thus in children the primary source of infection is in a 

 great many cases an otitis media, and Netter concludes 

 that infection takes place in such conditions from the nasal 

 cavities. 



Experimental Inoculation. Having thus seen that there 

 are present in the pneumonic processes and their complica- 

 tions certain organisms which possess distinct morphological 

 and biological characters, and of which by far the most 

 frequently present is Fraenkel's pneumococcus, we have 

 now to consider the evidence for their etiological relation- 

 ship to the disease. 



The pneumococcus of Fraenkel is pathogenic to various 

 animals. The susceptibility of different species varies to a 

 considerable extent. This point has been fully worked out 

 by Gamaleia. The rabbit, and especially the mouse, are 

 very susceptible ; the guinea-pig, the rat, the dog, and the 

 sheep, occupy an intermediate position ; the pigeon is quite 

 immune. In the more susceptible animals the general 

 type of the disease produced is not pneumonia, but a 

 general septiccemia. Thus, if a rabbit or a mouse be 

 injected subcutaneously with pneumonic sputum, or with a 

 scraping from a pneumonic lung, death occurs in from 

 twenty-four to forty-eight hours. There is some fibrinous 

 infiltration at the point of inoculation, the spleen is often 

 enlarged and firm, and the blood contains capsulated 

 pneumococci in large numbers (Fig. 55). If the seat of 

 inoculation be in the lung, there generally results pleuritic 

 effusion on both sides, and in the lung there may be a 

 process resembling in pathological characters the early stage 

 of acute croupous pneumonia in man. There are often also 

 pericarditis and enlargement of spleen. We have already 

 stated that cultures of the pneumococci on artificial media 

 in a few days begin to lose their virulence. Now, if such a 

 partly attenuated culture be injected subcutaneously into a 

 rabbit, there is greater local reaction, and pneumonia, with 

 exudation of lymph on the surface of the pleura, and a 

 similar condition in the peritoneum, may occur. In the rat 

 the results of inoculation are closely similar, and its 



