288 STREPTOCOCCUS-PNEUMOCOCCUS GROUP 



recovery as carriers, precisely as typhoid carriers harbor typhoid 

 bacilli after recovery from typhoid fever. 



Animal. Mice are the most susceptible of laboratory animals 

 to infection with the pneumococcus. Small amounts of pneumonic 

 sputum, exudate or pus injected subcutaneously lead to a rapidly fatal 

 septicemia. Encapsulated pneumococci are found in the blood and 

 visceral organs, particularly the spleen, which is enlarged, and the 

 peritoneal fluid. Rabbits are somewhat less susceptible and the 

 results of inoculation of pneumococcic exudates or cultures depend 

 upon the virulence of the organisms, the size of the dose, and the 

 method of inoculation. 1 The intravenous or subcutaneous inoculation 

 of virulent cultures leads to a fatal septicemia, death occurring within 

 five days as a rule. The less virulent organisms, which do not kill 

 the animal within a few days after inoculation, frequently cause 

 localized abscess formation with a fibrinous exudate. The nature 

 and extent of the lesions induced depend largely upon the time which 

 elapses between inoculation and the death of the animal. In general 

 it may be stated that localized lesions appear when less virulent 

 organisms are injected. Intravenous injections are more effective 

 than subcutaneous inoculations of the same amount of organisms. 

 Guinea-pigs are relatively non-susceptible to pneumococcus infection. 



Many attempts have been made to reproduce the typical patho- 

 logical lesions of lobar pneumonia in experimental animals. Wads- 

 worth 2 succeeded in reproducing typical lobar pneumonia in rabbits 

 by first partially immunizing them to the organism in order to localize 

 the lesions in the lungs. Lamar and Meltzer, 3 and Wollstein and 

 Meltzer 4 produced lobar pneumonia in dogs by the method of tracheal 

 insufflation devised by Meltzer; and Winternitz and Hirschf elder 5 

 have been equally successful in producing lobar pneumonia in rabbits. 

 The method consists essentially in forcing suspensions of pneumo- 

 cocci deep into the terminal bronchioles and their alveoli. Cole 6 

 has shown that the strain of organism influences the results ; organisms 

 of slight virulence give negative results, and organisms possessing too 

 great virulence cause a generalized septicemia with congestion and 

 edema of the lungs as the only local pulmonary manifestations. 



1 Kruse and Pansini, Zeit. f. Hyg., 1892, xi, 279 el seq. 



2 Am. Jour. Med. Sc., 1904, cxxvii, 851. 



3 Jour. Exp. Med., 1912, xv, 133. 



4 Ibid., 1913, xvii, 353, 424. 



5 Ibid., 1912, xvii, 657. 



6 Arch. Int. Med., 1914, xiv, 56. 



