486 A MANUAL OF BACTERIOLOGY 



in lactose serum broth, which the S. pneumonice does 

 not do. 1 



Both the S. pneumonice and the 8. mucosus are dissolved 

 by bile, a feature distinguishing them from the strepto- 

 cocci generally. 



Pathogenic action. The 8. pneumonice is pathogenic for 

 a number of animals, the most susceptible being mice, 

 then, in decreasing order, rabbits, rats, guinea-pigs and 

 dogs. Pigeons and fowls are immune. The virulence of 

 the organism varies considerably ; under cultivation it 

 may be completely lost, while by a series of passages 

 through a susceptible animal it may be much increased. 

 Death follows after subcutaneous, intravenous, intra- 

 peritoneal, or intrathoracic injection of a virulent culture, 

 or of rusty pneumonic sputum, into mice and rabbits in 

 twenty-four to forty-eight hours. The disease runs the 

 course of a septicaemia with high temperature and 

 dyspnoea, death being generally preceded by a subnormal 

 temperature and often convulsions. The post-mortem 

 appearances are much oedema and inflammatory infiltra- 

 tion at the seat of inoculation, haemorrhages in the serous 

 membranes, enlargement and congestion of the spleen, 

 and congestion of the lungs. The organisms occur in 

 large numbers in the blood, lungs, and spleen, usually in 

 the form of oval diplococci with well-marked capsules 

 (Plate XVII, a), but sometimes as short chains of strepto- 

 cocci. Cultures injected intratracheally into monkeys 

 induce a typical croupous pneumonia clinically and patho- 

 logically identical with that seen in man (Blake and 

 Cecil 2 ). All four of the types of pneumococcus react 

 similarly. Virulent cultures sprayed into the mouth and 

 nostrils of monkeys failed to produce pneumonia ; the 



1 See Holman, Journ. Path, and Bacter., vol. xix, 1915, p. 478. 



2 Journ. Exper. Med., 1920, vol. 31, pp. 403 et seq. (a series of important 

 papers). 



