566 VEGETABLE DRUGS 



vessels. The production of vascular contraction is denied 

 by some experimenters, but this statement is not substan- 

 tiated. 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 inflammatory con- 

 ditions by causing ischaemia. There are several kinds of 

 tannic acid, possessing slightly different chemical and physio- 

 logical properties. The official tannic acid — gallotannic 

 acid — is contained in nutgall and oak bark, while another 

 variety — catechutannic acid — is found iu kino, catechu, etc. 

 Action Internal — Tannic acid dries the mouth by closure 

 of glandular (mucous) ducts with (coagulated secretion, and 

 bv 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 diarrhoea. Tannic acid is converted 

 into gallic acid in the bowels and is absorbed and eliminated 

 in the urine as gallic and pyrogallic acids. Gallic acid does 

 not coagulate albumin or gelatin and has a very feeble 

 astringent action, so that tannic acid should always be used 

 for a local effect. The remote astringent influence of 

 tannic acid (in the form of gallic acid) is slight, but gallic 

 acid is preferable when an 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 

 diarrhoea, because they are less soluble (than tannic acid) 

 and the contained catechutannic 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 lesi<ms. In the form of 



