546 MICROBIOLOGY OF THE DISEASES OF MAN AND ANIMALS. 



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 barreirs at the entrance of the 

 nasal cavity in the obstructions 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 

 mentioned above, are also covered with ciliated cells which serve, to some 

 extent, 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, Bad. 

 diphtheria, M. intracellularis var. meningiiidis 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. They are being con- 

 stantly washed off the membrane by the saliva which contains a certain 

 per cent 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 are situated laterally between this cavity 

 and 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. 



The Lungs. In case infectious microorganisms pass down the trachea 

 and bronchi they meet first with the obstruction of the mucus which is 

 secreted upon the surface of these tubes. In addition, ciliated epithelium 

 is present, the wave motion of which moves from within out and 

 serves to cleanse the surfaces from microorganisms as in the nose. 

 Occasionally microorganisms lodge along the trachea and the bronchi 

 and produce slight irritations which if left undisturbed may immediately 

 produce serious infections. 



The Stomach. In case the microorganisms pass down the oesophagus 

 into the stomach, they immediately come into contact, in the normal 

 organ, with the gastric juice, which contains the hydrochloric acid in 

 such concentration that it is at least antiseptic if not germicidal. In 

 case the functional activity of the stomach is disturbed and the hydro- 



