478 BIOLOGY OF PNEUMOCOCCUS 



pneumococcal infection may be artificially reproduced in suitable 

 normal animals by the judicious parenteral introduction of pneu- 

 mococci or of their antigenic constituents. The properties of the 

 serum of artificially immunized animals may be transferred pas- 

 sively to normal animals. Owing to differences in the nature of the 

 immune substances in the serum of animals of diverse species, the 

 successful transference of passive immunity depends on the animal 

 selected as the source of the immune serum. 



During the development of immunity, whether evoked in a natu- 

 ral way or by artificial means, the tissue cells acquire a heightened 

 sensitivity to Pneumococcus and some of its derivatives. Hyper- 

 sensitivity in some animals may be manifested by an acute and 

 fatal anaphylactic reaction, by increased contractility of the 

 uterus, and by the inflammatory reaction of the cutaneous and 

 pulmonary tissues arising upon the appropriate introduction of 

 pneumococcal antigen. 



The induction of the hypersensitive state and elicitation of the 

 characteristic manifestations depend on the nature of the antigen 

 employed. It is the capsular polysaccharide of the pneumococcal 

 cell that orients the sensitizing stimulus and that is responsible 

 for the type-specificity of the visible phenomena. In the case of 

 hypersensitiveness to Pneumococcus, the allergic condition may be 

 suspended and the specific reactions prevented temporarily by the 

 introduction into the body of the polysaccharide homologous with 

 that of the antigen used to induce allergy. 



