CHAPTER VI 



PATHOGENICITY OF PNEUMOCOCCUS : 

 EXPERIMENTAL ANIMALS 



The ability of Pneumococcus to infect animals of different species 

 under natural circumstances or when experimentally introduced 

 by diverse routes into the animal body; the morbid manifestations 

 following pneumococcal infection in animals; virulence and other 

 factors influencing inf ectivity of pneumococci. 



Pneumococcus is incapable of producing disease in animals of 

 some species, while individual creatures exhibit different de- 

 grees of resistance to pneumococcal invasion. Variations in sus- 

 ceptibility or in resistance may be conditioned by special differ- 

 ences in anatomic structure, in genetic heritage, or in physiological 

 function, while individual differences may be due to both intrinsic 

 and extrinsic factors affecting the physical state of the animal be- 

 fore or at the time of inoculation. 



Susceptibility of the Animal Host 



THE RABBIT 



Rabbits are prone to develop spontaneous pneumococcal infec- 

 tion of the respiratory tract, contracting the disease from simi- 

 larly affected guinea pigs or from other rabbits.* Recovery from 

 the infection may be followed by the carrier state during which the 

 animal may serve as a potential source of infection to other stock 

 animals, while the presence of pneumococci in the nasopharynx 

 may constitute a confusing factor when the animal is used for ex- 

 perimental pneumococcal infection. 



Next to the mouse, the rabbit is the most susceptible of labora- 



* This is not an uncommon laboratory experience and among the references 

 at hand is that of Sanderson,! 218 w ho wrote of the spontaneous death of a rab- 

 bit from Pneumococcus following a supposedly air-borne infection in the labo- 

 ratory animal room. 



