690 MICROBIOLOGY OF DISEASES OF MAN AND DOMESTIC ANIMALS 



some of which are pathogenic. Their moist condition favors the growth 

 of microorganisms, but the mucus which is secreted upon them forms 

 a mechanical barrier to the bacteria and serves to wash them away. 

 This mucus is not germicidal but is perhaps slightly antiseptic. The 

 only mucous membranes of the body that are really exposed are those 

 of the eyelids, lips, anterior nares, genito-urinary apparatus and the anus. 

 It is perhaps more convenient to discuss these membranes in detail in 

 connection with the cavities which are connected with them. 



Nasal Cavity. Microorganisms find a barrier to the entrance of 

 the nasal cavity in the hairs which protect the anterior nares and 

 serve to keep out the dust from the inhaled air. The membranes of 

 the nasal tract, besides being covered with mucus, which acts as above 

 mentioned, are also covered with ciliated epithelial cells which move 

 from within out and serve to wash the mucus containing the bacteria 

 from the surface. Infections of the nasal mucous membranes are, 

 however, not uncommon. Bact. influenza, Strept. pyogenes, M. 

 pyogenes vars. aureus et albus, Bact. diphtheria, M. intracellularis var. 

 meningitidis , and occasionally Bad. mallei produce infection through 

 this membrane. 



The Mouth. The mouth probably contains the largest variety of 

 bacteria to be found anywhere in the body. A large number of these 

 bacteria are non-pathogenic, although pathogenic microorganisms do 

 occasionally occur. All the requisite conditions for bacterial growth are 

 provided in the mouth, namely, temperature, moisture and food. The 

 food supply is largely derived from materials which have been de- 

 posited during the process of mastication between the teeth and in the 

 various depressions of the mucous membrane. The microorganisms 

 also feed upon the desquamated squamous epithelial cells. They are 

 being constantly washed off the membrane by the saliva which contains 

 a certain portion of mucus. The saliva is not germicidal, and in all 

 probability only very slightly antiseptic. The most permeable part 

 of the mouth is in all probability the tonsils which separate this cavity 

 from the pharynx or throat. These lymphatic structures have many 

 deep crypts, and bacteria once entering the tissues of the tonsils may 

 gain access to the lymphatic circulation through these structures. 



In case bacteria are successful in passing the obstacles of protection 



. afforded in the nose and in the mouth and pass into the throat, there are 



two routes for their entrance into the internal body, namely, through 



