EXPERIMENTAL INOCULATION. 215 



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. The pneumococcus of 

 Fraenkel is pathogenic to various animals. The sus- 

 ceptibility of different species, as Gamaleia has shown, 

 varies to a considerable extent. 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. 61). 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 somewhat resembling 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 sub- 

 cutaneously into a rabbit, there is greater local reaction ; 

 pneumonia, with exudation of lymph on the surface of the 

 pleura, and a similar condition in the peritoneum, may 

 occur. In sheep greater immunity is marked by the 

 occurrence, after subcutaneous inoculation, of an enormous 

 local sero- fibrinous exudation, and by the fact that few 

 pneumococci are found in the blood stream. Intra-pul- 

 monary injection in sheep is followed by a typical pneu- 

 monia, which is generally fatal. The dog is still more 

 immune; in it also intra-pulmonary injection is follow.ed 

 by a fibrinous pneumonia, which is only sometimes fatal. 



