506 INFECTION AND IMMUNITY. 



questioned by many. Two factors would seem to 

 prevent their being carried to the alveoli by cur- 

 rents of inspired air: First, foreign bodies or in- 

 fected droplets are likely to strike and adhere to 

 the walls of the respiratory passages before they 

 have traversed a great length, and from this situa- 

 tion may again be carried out by the action of the 

 ciliated epithelium or coughing; the tortuous pas- 

 sages of the nose and its hairs and moist surfaces 

 arrest many micro-organisms. Second, the velocity 

 of the inspired air is greatly reduced or is nil by 

 the time the particles might have reached the 

 alveoli, a condition which renders their arrest all 

 the more probable. Nevertheless, pneumococci do 

 reach the alveoli, and by some it is supposed that 

 even in health they are carried there more or less 

 constantly and are as constantly destroyed. Occa- 

 sionally they have been found in the parenchyma- 

 tous tissue of the lungs of individuals who have 

 died of other than pneumococcus infections or of 

 non-infectious diseases. In order to show that 

 micro-organisms may be carried into the paren- 

 chyma by inspiration Nenninger allowed animals 

 to inhale a spray containing Micrococcus prodigio- 

 sus, and killing the animals after one-half hour, 

 was able to cultivate the coccus from the base of 

 the lungs where only alveoli and the finest bron- 

 chial branches were present (cited by Weichsel- 

 baum). 



- Various other agencies have been suggested by 



- which the cocci may be carried to the parenclryma- 

 Vtomi! tous tissue. For example, during the forced res- 

 piratory efforts which accompany coughing they 

 may be carried from the bronchial branches into 

 the alveoli. Or the organisms having reached the 



