SPECIFIGS FOR THE ALIMENTARY TRACT 



upon the bloodvessels supplying the glands, but this theory is not 

 usually given much credence. 



Astringents are divided into two great groups, the vegetable and 

 mineral. The former derive their action from their tannic acid 

 content, vfhile the latter are for the most part metallic salts. Most 

 astringents are also more or less irritant, especially if applied in 

 concentration, while some of the metallic members of the group 

 are more irritant than astringent. The irritation of the metallic 

 astringents is due to various conditions. In one instance it may be 

 due to the acid set free when the metal unites with the albumen of 

 the tissues, in another, to a very permeable membrane formed by the 

 salt, which does not prevent further action, and in still other cases 

 to the very toxic action of the metal itself. A few of the mineral 

 astringents appear to have a sedative or soothing effect. This is espe- 

 cially so of the bismuth salts, zinc oxide, and cerium oxalate. 



General Uses. Astringents are used to 1, cheek diarrhea; 2, 

 reduce inflammation of mucous membranes ; 3, promote healing ; and, 

 4, arrest hemorrhage. 



1. Check diarrhea. In this case, the astringents seem to act by 

 forming a deposit (tannates, albuminates) along the mucous mem- 

 brane of the bowel, which prevents absorption and also the penetra- 

 tion of other irritant material, thus overcoming irritation and check- 

 ing peristalsis, due to the irritation. At the same time they precipi- 

 tate the proteids of the superficial cells of the mucous membrane, 

 thus causing a shrinkage of the tissues and stoppage of secretion. 



2. Reduce inflammations of mucous membranes. The mucous 

 membranes most accessible for the application of astringents are 

 those of the mouth, pharynx, conjunctiva, nose, genito-urinary tract 

 and rectum. Tannic acid serves well in these cases, as also do the 

 soluble salts of zinc, silver nitrate and alum. The usual strength 

 for sprays and mouth washes are % to 1 per cent. ; for the vagina 

 or rectum, 1 to 2 per cent. ; conjunctiva and nose, Vs to Yi per cent. 



3. Promote healing. For application upon open wounds, ulcers, 

 etc., silver nitrate is very useful, then follow the soluble zinc salts 

 and alum. They are usually employed in V2 to 5 per cent, solutions, 

 but may also be used in dusting powders or in ointments (5 per 

 cent. ) . Caution should be used in applying some of them, especially 

 calomel and the lead salts as dusting powders, since they may be 

 absorbed sufficiently to produce toxic effect. Zinc oxide is entirely 

 safe and quite efficient. 



4. Arrest hemorrhage. All metallic salts and tannic acid prep- 

 arations arrest hemorrhage by precipitating the proteids, which stop 

 up the lumen of the small vessels, in a manner similar to normal 

 clotting by fibrin. This action will be discussed in detail under the 

 head of styptics. 



Principal members of the group of astringents are : 



