582 THE PNEUMOCOCCUS 



Intra-tracheal inoculation appears to do no harm, though Gamaleia after 

 irritating the respiratory passages by the injection of a solution of tartarated 

 antimony produced a fatal pneumonia by this method. 



The vitality and virulence of the pneumococcus become rapidly attenuated 

 by passage through sheep so that serial inoculations are impossible. 



Guinea-pigs. Guinea-pigs are comparatively immune to the pneumococcus. 

 Sub-cutaneous inoculation is followed by a more or less marked local reaction 

 which very often spontaneously resolves. Intra-peritoneal inoculation is 

 more severe and is often followed by death. 



Dogs. Dogs only succumb to extremely large doses. A very extensive 

 oedema is produced as the result of sub-cutaneous inoculation, and on rare 

 occasions death may take place about the fourth or fifth day : the blood 

 will contain a very few pneumococci. 



Intra-pulmonary inoculation sets up a pneumonia which runs the same 

 course as in man, but which as a rule resolves. 



Intra-tracheal inoculation is generally without effect : Tchistovich however 

 produced a fatal result in 3 out of 19 dogs inoculated by this method. In 

 performing the experiment great care must be taken that the tissues around 

 the trachea are not infected (for technique, see p. 179), otherwise the result 

 will be misleading. 



To summarize. The most susceptible animals die from a pneumococcal 

 septiccemia. Pneumonia occurs more often in the less highly susceptible animals. 

 Further, in accordance with the general ride, the severity of the infection is in 

 inverse ratio to the extent of the local lesion. 



SECTION II. MORPHOLOGY. 

 1. Microscopical appearance and staining- reactions. 



The pneumococcus presents under the microscope two different appear- 

 ances according as to whether it has been obtained from human or animal 

 tissues or from cultures on artificial media. In cultures on liquid albuminous 

 media (serum, or broth containing fresh blood, etc.) the pneumococcus has 

 however the same characteristics as in the tissues. 



A. Appearance in the tissues. The pneumococcus in sputum, blood, 

 scrapings of organs, etc. occurs as a coccus, sometimes rounded but generally 



^X 



k 



t^^g? 

 fe^ 



FIG. -274. Pneumococcus in sputum. Gram's stain and dilute carbol- 

 fuchsin. (Oc. 2, obj. T Uh, Zeiss.) 



