240 PATHS OF ENTRANCE OF PATHOGENIC ORGANISMS 



B. Mucosae directly continuous with the skin and lined with 

 stratified epithelium are commonly well protected thereby 

 and by the secretions. 



(a) The external auditory meatus is rarely the seat even 

 of local infection. The tympanic cavity is normally sterile^ 

 though it may become infected by extension through the 

 Eustachian tube from the pharynx {otitis media) . 



(b) The conjunctiva is frequently the seat of localized, 

 very rarely the point of entrance for a generalized infection, 

 except after severe injury. Those diseases whose path of 

 entrance is generally assumed to be the respiratory tract 

 (see ^' Lungs" below) might also be admitted through the 

 eye. Material containing such organisms might get on the 

 conjunctiva and be washed down through the lacrimal 

 canal into the nose. Experiment has shown that bacteria 

 may pass in this way in a few minutes. In case masks are 

 worn to avoid infection from patients suffering with these 

 diseases, the eyes should therefore be protected as well as 

 the nose and mouth. 



(c) The nasal cavity on account of its anatomical struc- 

 ture retains pathogenic organisms which give rise to local 

 infections more frequently than other mucosae of its charac- 

 ter. These may extend from here to middle ear, neighbor- 

 ing sinuses, or along the lymph spaces of the olfactory nerve 

 into the cranial cavity (meningitis). Acute coryza ("colds" 

 in man) is characteristic. Glanders, occasionally, is pri- 

 mary in the nose, as is probably roup in chickens, leprosy 

 in man. The meningococcus and the virus of poliomye- 

 litis pass from the nose into the cranial cavity without local 

 lesions in the former. 



(d) The mouth cavity is ordinarily protected by its epi- 

 thelium and secretions, though the injured mucosa is a 

 common source of actinomycosis infection as well as thrush. 

 In foot-and-mouth disease no visible lesion seems necessary 

 to permit the localization of the unknown infective agent. 



(e) The tonsils afford a ready point of entrance for ever- 

 present staphylococci and streptococci whenever occasion offers 

 (follicular tonsillitis, ''quinsy"), and articular rheumatism is 

 not an uncommon sequel. The diphtheria bacillus charac- 



