MEDICINES WHICH ACT ON TISSUE CHANGE 



455 



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

 yet iu 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 somewdiat 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 tho.se 

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

 advantage of solubility. 



Where the bowel discharges are of such a character 

 as to susaest 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 

 value and uses. 



Oak Bark. — The bark from young trees and the 

 smaller branches is preferred for medicinal purposes, as 

 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 frecjuently 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 



Fig. 428.— Niit-Galls 



1, 2, Nut-Galls 

 (Aleppo) from Quer- 

 cus infectoria. 3, 

 Transverse section. 



astring;ent or o-argle. 



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 



