180 BIOLOGY OF PNEUMOCOCCUS 



tory animals to pneumococcal infection. Susceptibility is greatest 

 for strains of Type I pneumococci, less for Type II organisms, and 

 still less for those of Type III. It should be remembered that later 

 studies have shown that while many strains of Type III pneumo- 

 cocci are avirulent for rabbits, there are others of the same type 

 that are highly pathogenic. 



It will be recalled that in the early days of bacteriology, Pas- 

 teur, 1065 " 6 Sternberg, 1816 " 8 Vulpian, 1453 and Claxton 237 produced a 

 fatal septicemia in rabbits by the subcutaneous injection of human 

 saliva containing, as we now know, pneumococci. With the excep- 

 tion of the intact skin, rabbit tissues present no barriers to the in- 

 vasion of virulent pneumococci ; the organisms, no matter by 

 which avenue introduced, soon reach the blood stream and, when in 

 sufficient numbers, cause the death of the animal. 



Bacteriemia is the predominant manifestation and pneumonia 

 develops only when the organisms are implanted in the lung by way 

 of the respiratory tract. The weakness of the rabbits' defense 

 against subcutaneous, intraperitoneal, or intravenous pneumococ- 

 cal inoculation is due, in part, to the comparative inability of the 

 leucocytes of the animal to engulf the invading cocci (Tongs, 

 1922 1416 ). Even when injected into the cisternal cavity of the 

 brain, as reported by Stewart (1927), 1322 septicemia rather than 

 meningitis ensues. As a rule, therefore, after artificial inoculation 

 with pneumococci, infection, unless it be by the intradermal or in- 

 tratracheal route, tends to become systemic and not localized. 



Subcutaneous inoculation. Neufeld (1901 ) 973 spoke of a pro- 

 gressive inflammation following the injection of pneumococci into 

 the subcutaneous tissues of the ear of the rabbit. When death did 

 not follow, necrosis was observed, and the infection appeared to 

 Neufeld to be similar to erysipelas, although Fraenkel, who had 

 previously observed the same effect, had not so considered it. 

 Cooper 276 found that the mucous membrane of the buccal surface 

 of the rabbit's cheek was susceptible to infection, but the inocula- 



