COCCACE.E AND THEIR PARASITIC RELATIONSHIPS 259 



fluid has been added forms an excellent medium. There is prac- 

 tically no growth below 25 C. On blood agar, the colony js 

 surrounded by a zone of greenish discoloration, a character of 

 great value in the early recognition of the pneumococcus isolated 

 from the body. The virulence of the microbe diminishes very 

 rapidly in artificial culture. Virulent material is best kept in 

 stock by preserving in a desiccator dried blood taken from a 

 rabbit dead of pneumococcus infection. The fluid blood may also 

 be kept in sealed capillaries in the refrigerator. By these methods 

 the virulence may be preserved for months. Rabbits, mice and 

 young rats are the most susceptible animals. 



The pneumococcus is the microbic agent in from 80 to 95 

 per cent of cases of acute lobar pneumonia. It also occurs in 

 otitis media, mastoiditis, meningitis, peritonitis and arthritis. 

 Its presence is usually associated with a fibrino-purulent exudate. 

 In severe pneumonia it is often present in the circulating blood. 



Pneumonia, or inflammation of the lungs, may be caused 

 by a great variety of organisms, the tubercle bacillus, the pneu- 

 mobacillus of Friedlaender, the streptococcus, the typhoid 

 bacillus and many others. Typical lobar pneumonia, however, 

 a disease characterized by a definite sequence of pathological 

 changes in the lung and by a rather typical clinical course, is 

 rarely caused by any organism other than Diplococcus pneumonia. 

 This is a very frequent disease in adults and doubtless the most 

 frequent cause of death in persons over 50 years of age. 



The nature of the poisons produced by the pneumococcus 

 is not definitely known. When killed by heat, the dead germ 

 substance is not very toxic. One very remarkable property of 

 the organism is its susceptibility to the action of bile and solutions 

 of bile salts. These cause a complete and prompt solution of 

 suspensions of pneumococci. Cole 1 has shown that a powerful 

 poison is set free by this disintegration of pneumococci, the 

 toxic action of which resembles that seen in the phenomenon 

 of anaphylaxis. 



1 Cole: Journ. Exp. Med., 1912, Vol. XVI, pp. 644-664. 



