140 INFECTION AND IMMUNITY. 



toxin of hay fever are readily absorbed from the 

 conjunctiva. 



Cavity. Compared with the anterior nares, the posterior 

 are poor in micro-organisms. This, in part, at 

 least, is due to the tortuosity of the channels, caus- 

 ing dust and bacteria to strike the walls where 

 they are held by a moist surface, and the action 

 of the ciliated epithelium in carrying them imbed- 

 ded in mucus, again toward the anterior nares. 

 Nevertheless, the nasal mucous membrane is a 

 common infection atrium for streptococci, staph- 

 ylococci, diphtheria and influenza bacilli, the dip- 

 lococcus of epidemic meningitis, and, probably, for 

 other infectious agents. 



Month. Very many species of micro-organisms flour- 

 ish in the oral cavity, some of them being patho- 

 genic: staphylococci, streptococci, pneumococci, 

 and often diphtheria bacilli. They are constantly 

 removed with the saliva, and through the exten- 

 sive desquamation of the epidermis occasioned by 

 mastication. Saliva is not germicidal, but in- 

 hibits the growth and weakens the virulence of 

 some bacteria. The fetid breath and the sor- 

 didity observed in fevers where the mouth is dry 

 are attributable at least in part to the lack of 

 saliva with its anti-infectious properties. The 

 great rapidity with which wounds of the mouth 

 heal is a potent factor in preventing serious infec- 

 tions. 



Micro-organisms do not readily reach the ulti- 

 mate ramifications of the bronchioles. In ordinary 

 respiration the velocity of the inspired air is so 

 reduced as it nears the alveoli that the further 

 movement of the gases is one of gradual diffusion 

 more than of violent admixture. Consequently 



