Pathogenic Bacteria 329 



distal end of each pair of cocci pointed or lance-shaped. Gram 

 positive and encapsulated. Optimum growth temperature of 

 37° C. Facultative aerobes. Habitat is the respiratory tract of 

 man and animals. Most common cause of lobar pneumonia. 



Whenever one speaks of pneumonia, the condition refers to any 

 inflammation of the lungs in which an exudate accumulates in the 

 alveoli (spaces of the lungs). More than 90% of the cases of 

 LOBAR PNEUMONIA are caused by Diplococciis pneumoniae, and this 

 same organism may be the etiological agent in otitis media 

 (middle ear infection), meningitis (infection of the membrane 

 covering the brain and spinal cord), peritonitis (inflammation of 

 the membrane lining the abdomen ) , and septicemia ( blood poison- 

 ing. ) The pneumococcus is not the only cause of lobar pneumonia; 

 any one of a number of other bacteria, rickettsiae, and viruses 

 might be involved. 



At least seventy-five different types of pneumococci have been 

 described, based solely upon serological differences demonstrable 

 in the capsular material of the organisms. The underlying diplo- 

 cocci are antigenically similar. Pneumococci are pathogenic for 

 mice and for rabbits, and if the bacteria are introduced into the 

 trachea of dogs and monkeys, these two animals contract a disease 

 resembling clinical pneumonia in human beings. 



Many persons are healthy carriers of pneumococci, and the 

 carrier rate increases during the colder months of the year when 

 respiratory infections are most prevalent. Transmission of the 

 disease appears primarily to be by droplet infection and by intimate 

 contact with carriers or infected individuals. Fatigue, undue ex- 

 posure, and nutritional deficiencies seem to predispose persons to 

 pneumonia, a disease which frequently follows a common cold that 

 has not been properly cared for. 



The capsular material of pneumococci is composed of a complex 

 sugar, called a polysaccharide, and because of the antigenic 

 specificity and the solubility of this capsular material, it is called 



SOLUBLE specific SUBSTANCE ( SSS ) . 



Before the advent of sulfanilamide drugs and antibiotics for 

 the treatment of pneumonia, it was necessary for physicians to treat 



