HOST RESPONSE TO ANTIGENIC ACTION 473 



organisms of that bacterial species, since a positive reaction has 

 been obtained in patients ill with other infectious febrile diseases. 



The capsular polysaccharides of Pneumococcus, on the other 

 hand, when injected intradermally into pneumonia patients are 

 highly type-specific in their action, and by their action serve as an 

 indicator of the immunological state of the individual tested. When 

 positive, the reaction is immediate, with wheal formation and the 

 development of erythema. Differing from the conditions observed 

 when pneumococcal protein or somatic carbohydrate are used as 

 test agents, reactivity of the dermal tissues is nearly always ab- 

 sent in normal human beings and in patients during the early 

 stages of pneumonic infection. As the disease progresses, usually 

 shortly before, during, or after crisis, the skin of the patient ac- 

 quires the capacity to react to the capsular polysaccharide and 

 the condition may persist for a shorter or longer time during and 

 after convalescence. A positive reaction is regarded as evidence of 

 definite immunological response on the part of the patient to the 

 infection. A positive reaction denotes that recovery is taking 

 place ; a negative reaction is interpreted as indicating that the de- 

 fensive forces of the body, whether natural or artificially aroused, 

 are unequal to cope with the infection. Intradermal tests with 

 type-specific polysaccharides, therefore, may be applied to esti- 

 mate the adequacy of serum treatment. 



The percentage of positive cutaneous reactions elicited by the 

 injection of homologous capsular polysaccharide varies with the 

 serological type of Pneumococcus responsible for the infection. 

 Almost all patients suffering from Type I infections react to the 

 Type I polysaccharide; approximately slightly more than one- 

 half the number of patients with Type II disease respond to the 

 intradermal injection of Type II polysaccharide; and in Type III 

 infections the percentage of positive reactors is even smaller. As 

 has been mentioned earlier in the text, the intradermal injection of 

 pneumococcal polysaccharides into human beings may induce sub- 



