592 VEGETABLE DRUGS 



vessels. Tannic acid causes arrest of leucocyte movements, 

 and diapedesis of the same, at the point of its application. 

 Tannic acid, although a slight local irritant to raw surfaces, 

 exerts a depressing action upon the sensory nerve endings, 

 and is essentially a sedative in inllammatory conditions l3y 

 causing ischaemia. There are several kinds of tannic acid, 

 possessing slightly different chemical and physiological prop- 

 erties. The official tannic acid — gallotannic acid — is con- 

 tained in nutgall and oak bark, while another variety — 

 eatechutannic acid — is found in kino, catechu, etc. 



Action Internal. — Tannic acid dries the mouth by clos- 

 ure of glandular (mucous) ducts with coagulated secretion, 

 and by constriction -of the surrounding parts. It lessens the 

 flow of mucus and of the digestive juices in the stomach and 

 intestines by the same process. The drug therefore inter- 

 feres with digestion for this reason, and also because it pre- 

 cipitates pepsin ; so that tannic acid should not be given 

 after eating. Moreover, the astringent action is arrested in 

 the stomach by combination with albuminous and gelatinous 

 material. Large doses irritate the alimentary canal and 

 may create vomiting and diarrha?a. Tannic acid is converted 

 into gallic acid in the bowels. Traces appear in the blood 

 and urine as sodium tannate which has no astringent action. 

 Of the tannic acid swallowed not more than 1 per cent, is 

 excreted in the feces and urine as tannic or gallic acid. All 

 the rest is oxidized in the body. Gallic acid does not coagu- 

 late albumin or gelatin and has a very feeble astringent 

 action — like that of any weak acid — so that tannic acid 

 should always be used for a local effect. The remote astrin- 

 gent influence of tannic acid (in the form of gallic acid) is 

 slight, but gallic acid is preferable when a remote astringent 

 action on the tissues of the body is desirable, since it is less 

 irritating to the mucous membrane of the digestive organs. 

 Catechu and kino are often chosen in place of tannic acid in 

 the treatment of diarrhcea, because they are less soluble (than 

 tannic acid) and the contained eatechutannic acid comes in 

 contact with the intestinal mucous membrane for a longer 

 time. The salts of tannic acid (tannates) are not astringent. 



Uses External. — Tannic acid is a valuable astringent in 

 a great variety of local inflammatory lesions. In the form of 



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