646 TANNIC ACID AND GALLS 



pale fawn. It requires for solution about one hundred parts 

 of cold water, three of boiling water, and twelve of glycerin ; 

 but is more soluble than tannic acid in alcohol and ether. 



ACTIONS AND USES. Galls and tannic acid differ only in 

 the degree of their action. They are astringent and anti- ! 

 septic. Galls have about one half the activity of tannic acid. 

 Gallic acid does not coagulate either gelatin or albumin, j 

 and it cannot be considered an astringent. It has no 

 medicinal properties. 



Tannic acid may be taken as the type of the group which 

 includes galls, oak bark, catechu, logwood, kino, and 

 rhatany. It has little effect on the unbroken skin ; but on 

 abraded, atonic, and hypersecreting skin and mucous 

 surfaces it coagulates albumin, causes dryness and tanning, 

 with some contraction of the soft textures. But, unlike 

 salts of lead, silver, or other mineral astringents, it does not 

 contract capillary vessels. The precipitate of albumin acts 

 as a protective, and diluted solutions hence relieve irritation. 

 It coagulates blood and arrests bleeding. In the mouth it 

 precipitates albumin on and in the superficial layers of the 

 epithelium, and so causes dryness and roughness. In the 

 stomach it again precipitates proteids forming tannate of 

 albumin, which is slowly digested, setting free the tannic 

 acid again, thus allowing the action on the mucous membrane 

 to continue both in the stomach and small intestine. Pepsin 

 and peptones in acid solution are not affected by tannic 

 acid. In excess, especially when the stomach is empty, 

 tannic acid causes irritation, with vomiting and even diarrhoea 

 in small animals. In moderate doses, the protective coat 

 of albumin and the lessening of glandular secretion, bring 

 about firmness of the faeces and constipation. The drug 

 has some antiseptic action, lessens fermentation, and renders 

 the faeces less offensive. It is slowly and partially absorbed, 

 as gallic acid or as an alkaline tannate, but when thus 

 neutralised it has very little astringent or haemostatic power. 

 It is excreted as gallic acid, or as some oxidised product 

 thereof. 



MEDICINAL USES. Tannic acid and galls, in powder, 

 solution, or spray, are applied in stomatitis, and relaxed 

 conditions of the pharynx and nasal passages. In diarrhoea 



