MUCOUS MEMBRANES. 



139 



Mucous 

 Membranes*. 



sistance is explainable, at least in part, by the 

 rapidity with which new connective tissue forms 

 in the subcutaneous tissue, offering a mechanical 

 limitation to the infection, and by the rich lymph 

 supply which makes possible the rapid accumula- 

 tion of bactericidal lymph and of phagocytic cells. 

 On the other hand, it must be mentioned that in 

 some diseases the subcutaneous tissue offers no 

 perceptible resistance to bacterial invasion 

 (plague), and that toxins may be more virulent 

 when introduced into this tissue than when in- 

 jected into the abdominal cavity or the general 

 circulation (tetanus). 



The moist condition of mucous membranes has 

 been found to favor the multiplication of many 

 microbes, although mucus itself is said to atten- 

 uate the virulence of some micro-organisms, as 

 the pneumococcus ; mucus, however, is not actively 

 germicidal. A layer of mucus, on the other hand, 

 is a mechanical protection, and its constant excre- 

 tion is a means of steadily removing bacteria from 

 mucous surfaces. 



The conjunctiva is protected against infection conjunctiva 

 by the mechanical interference of the eyebrows, 

 eyelashes, eyelids, irrigation of the conjunctival 

 surface by tears which carry germs through the 

 lachrymal duct into the nasal cavity, the ability 

 of the conjunctival epithelium to repair itself 

 rapidly, and the mild germicidal action of the 

 salts which are present in the tears. These pro- 

 tective agencies, however, are often surmounted 

 by micro-organisms, such as the pneumococcus, 

 staphylococcus and the influenza bacillus. Many 

 soluble poisons, aconite, diphtheria toxin and the 



