268 SPECIFIC MICRO-ORGANISMS 



The pneumococcus is the microbic agent in from 80 to 95, 

 per cent of cases of acute lobar pneum.onia. It also occurs in 

 otitis media, mastoiditis, meningitis, peritonitis and arthritis. 

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

 Ia 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 pneumonias. 

 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^ 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. 



It has been possible to induce a high degree of immunity in 

 horses, and the serum of these animals is protective and curative 

 in animal experiments. By use of such serum a large number of 

 serologically different strains of pneumococci have been recognized. 

 Cole and his associates have found that a considerable proportion 

 of labor pneumonia in New York City is caused by one of these 

 serological types, which they have designated as Group I, and they 

 have been able to produce an effective anti-serum against these 

 strains. A second, somewhat less homogeneous collection of 

 strains is characterized by specific reaction with another immune 



1 Cole: Journ. Exp. Med., 1912, Vol. XVI, pp. 644-664; Harvey Lectures, 1913- 

 14, Lippincott, p. 85. This paper gives references to literature. 



