249 QUERCUS INFECTORIA 



spaces being usually smooth ; they have a dark blueish-green or 

 olive-green colour externally, and are yellowish or brownish white 

 within, and have a small cavity in their centre, in which may be 

 found the remains of the larva or the more or less developed 

 insect, according to the period at which the galls have been 

 gathered. They have no odour, but an intensely astringent and 

 somewhat acidulous taste, which is ultimately followed by some 

 degree of sweetness. White galls are those from which the fly 

 has escaped, hence they are perforated from the surface to the 

 central cavity (which is here sometimes as much as a quarter of 

 an inch in diameter) by a small circular canal. They are larger 

 than the blue galls, lighter coloured, being pale yellowish brown, 

 less compact, less heavy, and are not so astringent ; they are of 

 inferior value. 



The most important constituent of nutgalls is that kind of 

 tannic acid which from having been first distinguished in them is 

 called gallo-tannic acid. The best galls yield from 60 to 70 per 

 cent, of this tannic acid, although in some cases not more than 

 about 30 per cent, is obtained. Galls also contain 3 or more per 

 cent, of gallic acid, together with sugar, resin, and other unimport- 

 ant substances. Infusion of galls reddens litmus paper, forms an 

 inky compound on the addition of a persalt of iron, and a 

 yellowish-white precipitate with a solution of gelatine. 



Medical Properties and Uses. Galls are the most powerful of 

 known vegetable astringents, hence they are applicable in all cases 

 where astringent medicines are required. In their crude state 

 they are, however, but little used, except externally, but the 

 official tannic and gallic acids which are obtained from them, 

 are much more largely employed medicinally. In the form of 

 decoction or when powdered, galls have been recommended as 

 an antidote in poisoning by emetia and the vegetable alkaloids 

 generally ; also in that of those vegetable products as opium, 

 colchicum, nux vomica, &c., the activity of which depends on an 

 alkaloid ; and in poisoning by tartarated antimony. The powers 

 of galls, however, as an antidote, require further investigation. 

 The official tincture of galls when diluted with water forms a 



