CHAPTER XII 



HOST RESPONSE TO ANTIGENIC ACTION 

 OF PNEUMOCOCCUS 



Normal barriers to the invasion and multiplication of pneumo- 

 cocci in the animal body; the immunological reaction naturally 

 stimulated by pneumococcal infection and the reaction artificially 

 aroused by the administration of pneumococci, their constituents, 

 or derivatives; the somatic manifestations of the immune state; 

 and the utilization by the body of antibodies passively acquired. 



Sound skin and healthy mucous membranes are impediments to 

 the entrance of Pneumococcus into the animal body. Under- 

 lying these tissues, as a line of secondary defense, are the leuco- 

 cytes, which with normal auxiliary elements of the blood may in- 

 gest and destroy the invading cocci. The localization or the sys- 

 temic distribution of the organisms depends on the vigor of the 

 phagocytic response and on the functional capacity of the body 

 to elaborate specific antibodies in response to the antigenic stimu- 

 lus provided by the invading microorganisms. 



Total failure of the defenses means death but, with only a par- 

 tial lack of antagonistic factors, the animal may pass through the 

 rigors of pneumococcal disease and thereby acquire greater, if 

 temporary, resistance to subsequent attacks. An analysis of the 

 protective mechanism of the animal economy against pneumo- 

 coccal infection will be attempted in the present chapter. 



Natural Immunity 



IN ANIMALS 



A reason for the behavior of various normal animals toward 

 pneumococcal infection was sought by Tchistovitch (1890), 1381 

 who subjected dogs, rabbits, and mice to subcutaneous, intra- 

 tracheal, and intraocular inoculation with Streptococcus lanceo- 



