PNEUMONIA, MENINGITIS AND GONORRHEA 325 



Immunity. — The problem of immunization against pneu- 

 monia is complicated by the variety of types of pneumocoeci 

 and other organisms causing the disease. It is also compli- 

 cated by the marked variation which pneumocoeci appar- 

 ently may show in virulence and by the great differences 

 which may occur in resistance or immunity to the disease. 

 Specific antisera have been prepared for certain types by 

 injecting horses or other suitable animals, first with killed 

 and finally with living cultures of pneumocoeci. The use 

 of a potent antiserum against the right type of microorgan- 

 ism has proved markedly advantageous. Difficulty in typ- 

 ing organisms and in the preparation of potent antisera has 

 interfered with its widespread use. 



Pneumocoeci together with streptococci have generally 

 been included in considerable numbers in the vaccines used 

 to prevent influenza or rather to prevent the development 

 of secondary complications following attacks of influenza. 

 The evidence concerning the value of these vaccines is very 

 conflicting. 



Immunity against pneumonia apparently is short-lived. 

 While a person convalescing from the disease may show 

 evidence of a high degree of acquired immunity, this usually 

 does not persist for a very long period. 



Neisseria gonorrhce^ 



Synonyms. — Micrococcus gonorrhoem, Diplococcus gonor- 

 rlicece. 



The causal name usually applied is gonococcus, occa- 

 sionally diplococcus of Neisser. 



The disease produced is gonorrhea in man, not transmis- 

 sible to animals. 



Morphology. — Stained mounts of gonorrheal pus show 

 the Gram-negative, coffee-bean-shaped diplococci, lying gen- 

 erally in pairs inside the polymorphonuclear leucocytes. 

 In culture there is little or no tendency to chain formation, 



