THE PNEUMOCOCCUS 103 



The pneumococcus is closely allied to the streptococcus, 

 from which it is sometimes hard to distinguish. 



This is the germ which is responsible for most of the 

 cases of lobar pneumonia and for more than half of the 

 other forms of pneumonia. Other infections in which 

 the pneumococcus is frequently the causative agent 

 are pleurisy, otitis media, with its complicating mas- 

 toiditis, meningitis, endocarditis (inflammation of the 

 valves of the heart), rhinitis (inflammation of the nasal 

 passages), tonsillitis, arthritis (inflammation of joints), 

 and conjunctivitis and keratitis (inflammation of the 

 outer covering of the eyeball). 



Usually when the pneumococcus invades the lungs an 

 extensive inflammation of the lungs results. If the inflam- 

 mation involves an entire lobe or more it is spoken of as 

 a lobar pneumonia; when it is scattered throughout the 

 lung it is called a bronchopneumonia. 



In pneumonia there is a marked pouring-out into the 

 air spaces of leukocytes, serum, and fibrin. Mixed with 

 this are degenerated epithelial cells from the air spaces, 

 red blood-cells, pneumococci, and cell debris. The affected 

 lobe becomes almost solid and may be compared to a 

 sponge which has been saturated with pus. There is much 

 absorption of poison from all this material, hence the high 

 fever, delirium, rapid pulse, etc. If the patient recovers 

 the lung gradually resumes its normal condition, the exu- 

 date being absorbed and carried off by the scavenger cells 

 of the body (white blood-cells). Some of it, to be sure, is 

 expelled by coughing. 



In pneumonia the pneumococci are found in enormous 

 numbers in the sputum; in otitis media, in the pus dis- 

 charged from the ear; in rhinitis it is in the nasal secre- 



