CHAPTEE XIII [423] 



IMMUNITY OF THE SKIN AND MUCOUS MEMBRANES 



Protective function of the skin. Exfoliation of the epidermis as a means of ridding 

 the animal of micro-organisms. Localisation and arrest of micro-organisms in 

 the dermis. Intervention of phagocytes in the defence of the skin. 



Elimination of micro-organisms by the conjunctiva. Microbicidal function of the 

 tears. Absorption of toxins by the conjunctiva. Protection of the cornea. 

 Elimination of micro-organisms by the nasal mucosa. Protection by the respi- 

 ratory channels. Dust cells. Absorption of poisons by the respiratory channels. 



Alleged microbicidal property of the saliva. Part played by microbial products in 

 the protection of the buccal cavity. Antitoxic function of the saliva. 



Antiseptic action of the gastric juice. Antitoxic function of pepsin. 



Protective function of the alimentary canal. Absence of microbicidal power from the 

 intestinal ferments. Protective function of the bile. Antitoxic r6le of the 

 digestive ferments. Favouring and retarding functions of the intestinal micro- 

 organisms. Destruction of toxins by these micro-organisms. 



Defensive role of the liver. Protective function of the lymphoid organs of the 

 alimentary canal. 



Protective function of the mucous membrane of the genital organs. Autopurifica- 

 tion of the vagina. 



IN the preceding chapters the phenomena of immunity which are 

 exhibited within the animal body in which the portals were open for 

 the penetration of the micro-organisms and their poisons have been 

 studied. We had to deal almost exclusively with experimental im- 

 munity, the study of which constitutes the basis of our present 

 knowledge concerning the general problem of immunity. In natural 

 immunity, however, things do not follow the same course. The micro- 

 organisms and their toxins are not introduced directly into the tissues 

 and blood by means of a syringe or other instrument. The micro- 

 organisms have to make their own way through the skin and the 

 mucosae, tissues which offer a resistance more or less serious and 



262 



