VIRULENCE. 505 



Rosenow and others have shown that virulent virulence. 

 pneumococci are much less susceptible to phago- 

 cytosis than are non-virulent strains. 



By autolysis the substance on which the non- 

 susceptibility of virulent pneumococci to phago- 

 cytosis depends, can be removed and in this man- 

 ner virulent pneumococci rendered readily phago- 

 cytable. Furthermore, by treating avirulent 

 strains of organisms with the autolytic products 

 of virulent organisms, the readily phagocy table 

 non-virulent pneumococci can be rendered less 

 susceptible to phagocytosis. This substance, which 

 can be extracted from pneumococci and on which 

 the resistance to phagocytosis depends, Rosenow 

 has called "virulin." Virulin resists boiling for 

 two minutes and is insoluble in alcohol and ether. 



The pneumococcus is present in the nose, mouth occurrence 

 and pharynx of a large percentage of individuals. * 

 It is encountered more frequently in crowded cities 

 than in country districts. It persists for weeks 

 and months in the mouths of convalescents from 

 pneumonia, and it reaches the mouths of those 

 who are in the vicinity of pneumonics. It is found 

 frequently in the conjunctiva and occasionally in 

 the deeper air passages. That it may reach the 

 stomach and intestines with the sputum is appar- 

 ent, and it has been found there as the cause of 

 diphtheric enteritis, a condition which may be 

 followed by pneumococcus peritonitis or general 

 infection. 



The lungs are infected by inhalation of the Entrance 

 cocci. Suspended in droplets of saliva or mucus, into 

 or adherent to foreign particles, they may be car- 

 ried fairly deeply into the bronchial tubes. That 

 they ever reach the alveoli by this means alone is 



