DIPLOCOCCUS PNEUMONIA 97 



in pairs, with the distal ends pointed (lance-shape), and 

 being surrounded by a capsule. This shape and envelope 

 are quite characteristic, and almost determinative. The 

 coccus grows very slightly on ordinary culture media, but 

 best when blood or blood-coloring matter is added. It then 

 produces a faint green color and grows best at 37 C. or 98 F., 

 but does not live long, requiring repeated transference to 

 fresh food. In sputum the pneumococcus may remain alive 

 and capable of producing disease for several months if pro- 

 tected from light. If the sputum be dried and powdered, 

 so that it could be inhaled, the cocci live for a few days in 

 diffused light. Direct sunlight kills them almost immediately. 

 They are killed at 52 C. or 126 F. in ten minutes. It is 

 said that the best way to disinfect sputum is by the addition 

 of about one-third alcohol. The pneumococcus itself has a 

 very low resistance to any of the ordinary disinfectants, 

 being killed in a few minutes. 



Most of the lower animals, particularly mice and rabbits, 

 but not birds, are susceptible to the pneumococcus. How- 

 ever, a true pneumonia as seen in man has not been produced 

 artificially. The pneumococcus produces a small quantity 

 of poison aside from itself, but acts chiefly by reason of sub- 

 stances within the germ cell. It has been found that there are 

 four closely related varieties of pneumococci capable of caus- 

 ing pneumonia and that against one of them it is possible 

 to produce in horses a powerful antiserum. In a given case 

 of pneumonia the causative strain of cocci is isolated and 

 studied; if it belongs to the type for which the antiserum is 

 available this may be injected under the skin or into a vein. 

 The death-rate of pneumonia for this one type has been 

 somewhat reduced by the serum treatment. The use of 

 vaccines therapeutically has not been followed by uniformly 

 favorable results, but prophylaxis by this means seems to 

 hold out some promise. The blood in pneumonia contains 

 some agglutinins, but they are not of much value in diag- 

 nosis. 

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