EXPERIMENTAL INOCULATION 235 



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. 



As bearing on the occurrence of pneumococcal infections 

 .secondary to such a local lesion as pneumonia, it is important to 

 note that in a large proportion of cases of the latter disease the 

 jineumococcus can be isolated from the blood. 



Experimental Inoculation. The pneumococcus of Fraenkel is 

 pathogenic to various animals, though the effects vary somewhat 

 \vith the virulence of the race used. The susceptibility of 

 different species, as Gamaleia has shown, varies to a considerable 

 extent. The rabbit, and especially the mouse, are very sus- 

 ceptible ; the guinea-pig, the rat, the dog, and the sheep 

 occupy an intermediate position ; the pigeon is 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 

 tibrinous infiltration at the point of inoculation, the spleen is 

 often enlarged and firm, and the blood contains capsulated 

 pneumococci in large numbers (Fig. 69). If the seat 'of inocula- 

 tion 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 pneumococcus 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 

 pit-lira, 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-pulmonary injection in sheep is 

 followed by a typical pneumonia, which is generally fatal. The 

 dog is still more immune ; in it also intra-pulmonary injection is 

 followed by a fibrinous pneumonia, which is only sometimes 

 fatal. Inoculation by inhalation appears only to have been 

 performed in the susceptible mouse and rabbit; here also 

 septicaemia resulted. 



The general conclusion to be drawn from these experiments 

 thus is that in highly susceptible animals virulent pneumococci 



