immunity of the skin and mucous membranes 417 



factor. Just as on the surface of the skin, the corneal cells are in a 

 permanent state of desquamation, so the cells in the mouth are being 

 constantly renewed. This desquamation increases especially during 

 mastication, when enormous numbers of cells are thrown off; after 

 every meal there is a partial renewal of the surface of the lining 

 of the buccal cavity. Being covered on their surface, and in their 

 interstices charged with innumerable micro-organisms, the epithelial 

 cells carry away with them all this population from the mouth. 



The numerous micro-organisms which persist in the mouth, in 

 spite of all these means for getting rid of them, must also play 

 a certain part in the defence against infections. It is very probable 

 that many of these saprophytes impede the multiplication of certain 

 pathogenic bacteria ; but at present it is impossible to define more 

 exactly these phenomena of microbial competition. It is only because 

 we have analogies in other regions of the body that we are able to 

 defend this position. 



The saliva, incapable of destroying the micro-organisms them- 

 selves, is able to act on their soluble products, as on certain other 

 poisons. In this relation the action of the saliva on snake venom is 

 most familiar. Wehrmann^, who has made researches on this subject 

 in Calmette's laboratory at Lille, has shown that the amylase (ptyalin) 

 of human saliva, mixed with very rapidly fatal doses of venom, quite 

 prevents its toxic action. Von Behring^ reminds us on this point 

 that the ancient Psylli (a race of northern Africa), at the beginning [438] 

 of our era, employed their saliva as an antidote against snake 

 bites. 



Powerless to kill the micro-organisms, the saliva carries them off 

 mechanically to the exterior or, more frequently, into the stomach. 

 The acid medium of this great reservoir exerts a very marked effect 

 on these microscopic organisms. It has long been recognised that the 

 gastric juice prevents putrefaction and can arrest it even when it has 

 become very advanced. From this observation an antiseptic action of 

 this juice was inferred. Bacteriological researches, undertaken to 

 determine the nature of this action, have demonstrated that several 

 species of micro-organisms die very shortly after being placed in con- 

 tact with the gastric juice in vitro* Straus and Wurz^ found that even 



1 Ann. de VInst. Pasteur, Paris, 1898, t. xii, p. 510. 



2 " Allgemeine Therapie der Infectionskrankheiten," in Eulenburg u. Samuel's 

 " Lehrb. d. allg. Therapie," Berlin u. Wien, 1899, Bd. in, S. 980. 



3 Arch, de med. exper. et d'anat. path., Paris, 1889, 1 1, p. 370. 



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