PNEUMOCOCCUS 131 



after quite a length of time. On glycerine agar it grows better, 

 but the colonies are small and difficult to see. In both, the colonies 

 are whitish, with a pearly lustre. On blood serum it grows in trans- 

 parent colonies. In bouillon it grows feebly, with a whitish sedi- 

 ment, and in the form of chains. Here the growth is inhibited by 

 the products of its own metabolism, i.e., lactic acid. If this is neu- 

 tralized by putting chalk into the bouillon the growth becomes 

 luxuriant and the bouillon becomes thick. On potato it will not 

 grow. It ferments some of the sugars, the most important being 

 inulin. No gas is formed. 



Habitat. Outside the human body it has not been found, but is 

 normally present in the mouth of about 30 percent of all people. 

 Even the alveoli of the lungs in health contain them. Human saliva 

 injected into animals often causes pneumococcic septicaemia. They 

 are also found on the conjunctiva and nose in health. 



Chemical Activities. No soluble toxin has been discovered. 

 The toxic properties are due to an endo-toxin. This organism is 

 a pyogenic one, and causes dense fibrinous exudates on serous 

 membranes. All tissues of the body may be attacked. Some 

 strains of pneumococci are more neurotoxic than others. 



In rabbits an injection (intravenous) of pneumococci very often 

 (33 percent) causes lobar pneumonia; certain strains cause lobular 

 pneumonia habitually among the susceptible animals (Eyre). In 

 human infection the organisms are forcibly inhaled into the deepest 

 recesses of the lungs. Pneumonia may be haematogenous in origin 

 also. 



Besides pneumonia, any serous membrane may be attacked and 

 pleuritis, peritonitis, pericarditis, or meningitis may be caused. 

 Abscesses anywhere may be due to the pneumococcus. Mucous 

 membranes of the throat of ten "are affected; middle ear abscesses 

 also may be caused by this organism. Pneumococcic septicaemias 

 are common. 



During pneumonia, pneumococci may be recovered from the 

 blood before the crisis by means of blood cultures; 10 c.c. of blood 



