148 BACTERIA 



will not grow. It ferments some of the sugars, the most impor- 

 tant and characteristic being inulin. No gas is formed. Pneu- 

 mococcic are soluble in bile or a solution of its salts, a distinguishing 

 determinative character. 



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

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

 In apparent health cultures from the throat or the sputum in- 

 into animals often causes pneumococcic septicaemia because 

 Type IV (see page 76) may be frequently found in them. The 

 so-called "fixed types" I, II, and III occur in the throat during 

 pneumonia but disappear shortly after recovery. It also may be 

 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 exu dates on serous 

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

 strains of pneumococci are more neurotoxic than others. 



In rabbits an intravenous injection of pneumococci will cause 

 a septicaemia with at times areas of lobular pneumonia. The 

 only successful reproduction of pneumonia in the lower animals 

 is accomplished by tracheal insufflation of pure virulent cultures. 

 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 often 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 

 abstracted from veins is mixed with 500 c.c. of milk or bouillon 

 and incubated. In twenty-four hours pneumococci, if present, 



