ANTIGENICITY OF PNEUMOCOCCUS 349 



to infection than did those that had not been so fed. In a second 

 communication (1932), McDaniels 877 reported attempts to ascer- 

 tain the details of the immunological mechanism operating in 

 orally immunized rats. Normal control rats and rats previously 

 injected with egg-white and Type I pneumococcal autolysates were 

 inoculated intraperitoneally with one hundred fatal doses of a 

 virulent, homologous strain of Pneumococcus. All the normal rats 

 died within two to four days, while 96 per cent of the vaccinated 

 animals survived. Although the leucocyte count was subject to 

 wide fluctuations, the immunized rats, six hours after inoculation, 

 always showed an appreciably higher white-cell count than did the 

 unvaccinated controls. In none of the vaccinated rats which sur- 

 vived infection could pneumococci be demonstrated in the blood, 

 although pneumococcemia was present in all the animals that suc- 

 cumbed. 



Ross (1931 ) 1188 described the comparative immunizing action of 

 soluble specific substance and of whole or dissolved pneumococci 

 when fed to rats. One feeding of Type I SSS sufficed to protect 

 the test animals against intraperitoneal injection of virulent Type 

 I organisms, and the increased type-specific resistance was com- 

 parable, with slight quantitative differences, to that following the 

 oral administration of intact or dissolved pneumococci. Ross failed 

 to immunize mice by a similar procedure and attributed the failure 

 to some cell constituent active in the mouth of mice. In other 

 papers (1932), Ross 1189 " 90 reported that the capsular polysaccha- 

 ride of Type II Pneumococcus was incapable, when introduced by 

 the oral route, of increasing the resistance of rats to infection. 

 The soluble specific substance of Type III organisms induced pro- 

 tection in rats to organisms of the homologous type but the per- 

 centage of animals so protected was less than in the case of 

 animals receiving the whole or intact cell by mouth. When the spe- 

 cific polysaccharide of Type I Pneumococcus was fed to rats, no 

 immunity against Type II or Type III organisms was obtained, 

 and the ingestion of SSS of Types II and III did not protect the 



