MEDICINES WHICH ACT ON TISSUE CHANGE 



455 



Nut-Galls. Although tannic acid is extracted from nut-galls (fig. 428), 

 yet in practice we find powdered galls have certain advantages over the 

 active principle for some purposes, while tannic acid is best suited to others. 

 Powdered galls are less astringent than tannic acid, and rather more so 

 than oak bark, elm bark, or catechu. They are not absorbed with the 

 facility of alum, or iron, but have the effect of coagulating albumen. In 

 horse practice they are used in electuaries for relaxed and sore throat, 

 and abrasions of the mouth and fauces generally, where a somewhat con- 

 stringing effect is desired from an agent that is not likely 

 to be taken up into the circulation. The powder is also 

 prescribed with success, as a ball, in cases of polyuria 

 or profuse staling. 



Tannic Acid. The action and uses of tannic acid, 

 or tannin as it is sometimes called, are similar to those 

 of nut-galls above described, but it has the additional 

 advantage of solubility. 



Where the bowel discharges are of such a character 

 as to suggest abraded surfaces, tannin is administered 

 with great advantage not only on account of its power 

 to check secretion, but also because of its action on the 

 bleeding vessels. It is soluble in water and spirit, and 

 has a special affinity for glycerine. 



Gallic Acid. This astringent is nearly allied to 

 tannic acid, both in chemical composition and therapeutic Fi 428 _Nut 

 value and uses. 1( 2> Nut . Galls 



Oak Bark. The. bark from young trees and the (Aleppo) from Quer- 



, r -i r T--, cus infectoria. 3, 



smaller branches is preierred lor medicinal purposes, as Transverse section. 



containing a relatively larger amount of the astringent 



principle than is to be found in other portions. It has a special value 



in the treatment of chronic diarrhoea and bowel discharges of a dysenteric 



type. It is usually prescribed in the form of decoction, both as 



an internal remedy and as an application to languid sores and indolent 



ulcers. 



Catechu is a vegetable extract of special value as a bowel astringent, 

 and is frequently combined with opium and chalk. It is prescribed as 

 a powder, tincture, and infusion. 



Kino is similar in its action, and chiefly employed as an intestinal 

 astringent or gargle. 



Alum. There are a number of compounds of alumina, but that com- 

 monly known as " alum " is a sulphate of ammonia and alumina. Veteri- 

 nary surgeons value the drug highly, and employ it for a variety of 



