EXPERIMENTAL INOCULATION 581 



of them be due to the pneumococcus, though it is to be remembered that they may 

 be caused equally by any of the other organisms of suppuration. 



(v) Over and above such cases as these in which pneumonia is a co-existent 

 symptom, the pneumococcus may also be the primary cause of fibrino-purulent 

 pleurisy, sero-fibrinous or suppurative pericarditis (Osier, Banti), conjunctivitis, 

 keratitis, suppurative otitis (Zaufal, Netter), ulcerative endocarditis (Jaccoud and 

 Netter, Weichselbaum), simple or membranous inflammation of the throat (Cornil, 

 Jaccoud, Menetrier, Rendu and Baulloche), peritonitis, and suppuration of the 

 biliary passages. 



(vi) The pneumococcus is also the primary cause of a large number of cases of 

 meningitis, frequently of the cerebro-spinal type : Netter found this organism in 

 eighteen out of thirty- one cases of meningitis neither accompanied nor followed by 

 pneumonia. 



The pneumococcus is the cause of a small minority of cases of epidemic cerebro- 

 spinal meningitis (Foa, Landouzy) though it is now well known that epidemic 

 cerebro-spinal meningitis is usually due to the Meningococcus (q.v.). 



Marchoux has described an epidemic of cerebro-spinal meningitis among the 

 natives of Senegal which occurred coincidently with numerous cases of pneumonia 

 and which was caused by the pneumococcus. 



SECTION I. EXPERIMENTAL INOCULATION. 



Mice are the most susceptible animals : then in order of decreasing suscepti- 

 bility come rabbits, rats, sheep, guinea-pigs and dogs. Pigeons are immune. 



Mice. Sub-cutaneous inoculation of a small quantity of a culture of the 

 pneumococcus or of a pneumococcal exudate invariably leads to the death 

 of the animal in 12-30 hours. Mice succumb as the result of a pneumococcal 

 septicaemia without showing any pulmonary symptoms : at the site of inocula- 

 tion only is there a little oedema. Post mortem, there is no lesion other than 

 an enlargement of the spleen : the blood is black and contains a large number 

 of encapsulated pneumococci, as do also the spleen and other internal viscera, 

 the peritoneum and bone marrow. 



Rabbits. The inoculation of rabbits may be productive of either one of 

 two types of disease according to the virulence of the organism inoculated. 



(a) Inoculation of a virulent virus. Sub-cutaneous, intra-peritoneal or 

 intra-venous inoculation leads to the death of the animal from septicaemia 

 in 24-72 hours. There is only a slight local reaction. Post mortem the spleen is 

 enlarged and the pneumococcus may be found in the blood and internal organs. 



Lobar pneumonia often accompanied by pleurisy on the same side follows 

 inoculation of material into the lung. 



(b) Inoculation with an attenuated virus. Sub-cutaneous inoculation proves 

 fatal though much less rapidly than in the former case. There is an inflam- 

 matory reaction at the site of inoculation and the animal dies, not from a 

 septicaemia without visceral localization, but from a true lobar pneumonia 

 frequently accompanied by pleurisy, pericarditis, peritonitis, arthritis, etc. 



Rats. Rats only succumb after the inoculation of very much larger quan- 

 tities of the virus than are necessary to kill mice and rabbits. There is an 

 intense inflammatory reaction at the site of sub-cutaneous inoculation, and 

 the oedema may extend over the whole of the abdominal and thoracic walls : 

 lobar pneumonia not infrequently results. Post mortem only a few pneumo- 

 cocci are found in the blood. Intra-pulmonary inoculation produces a patch 

 of lobar pneumonia accompanied by a sero-fibrinous pleurisy. 



Sheep. To produce a fatal infection in sheep by sub-cutaneous inoculation 

 more than 1 c.c. of culture must be used. An extensive oedema develops 

 around the site of inoculation : when death takes place only a few micro- 

 organisms are found in the blood. 



Intra-pulmonary inoculation is followed by a fatal attack of pneumonia. 



