HOST RESPONSE TO ANTIGENIC ACTION 443 



and resisted heating at 65° for one hour, but was destroyed after 

 heating for the same period at 75°. No dialysis of the enzyme 

 could be demonstrated. The activity of the enzyme persisted in 

 concentrations of sodium chloride varying from normal to thirty- 

 two times normal. In exudates, antigenic substances were also 

 found, evidently arising from the dissolution of pneumococci in the 

 infected lung. The presence of specific precipitinogen was disclosed 

 when the exudate was mixed with homologous antipneumococcic se- 

 rum. After testing extracts of affected lungs, Lord and Nye 833 fur- 

 ther concluded that the pneumonic lung contained a soluble sub- 

 stance inhibiting agglutination of fixed types of pneumococci by 

 homologous serum. An analogous substance was found by Ward 

 (1932) 1483 in the filtrate of a lung obtained at necropsy from a pa- 

 tient dying from pneumonia due to Type III Pneumococcus. The 

 substance was similar to that present in somewhat lower concen- 

 tration in broth cultures of Type III Pneumococcus which dis- 

 played powerful antibactericidal action. 



Artificially Induced Immunity 



The antigenic properties of Pneumococcus and the manifesta- 

 tions of the immunological reaction of the animal body to anti- 

 genic stimuli have already been treated in the text in some detail. 

 However, in order that the presentation of the features of the ani- 

 mal hosts' response may be orderly and complete, a brief synopsis 

 is made at this point of the factors that are chiefly concerned in 

 the artificial production of the immune state. 



ACTIVE IMMUNITY 



The ability of pneumococcal materials, purposely introduced, to 

 raise the resistance of susceptible animals to infection with Pneu- 

 mococcus, with the accompanying elaboration of demonstrable 

 specific immune substances or antibodies, is dependent upon the 

 nature of the material employed and also upon the special racial 

 and individual peculiarities of the animal treated. The more 



