454 HEALTH AND DISEASE 



course of arsenic, especially if given during the moulting period, may have 

 the effect of checking its eruption. 



In the chronic cough of broken wind, arsenic has been found a valuable 

 remedy. 



ASTRINGENTS 



Astringents are agents whicli cause constriction or contraction of the 

 tissues to which they are applied, and diminish the amount of secretion 

 from mucous membranes. 



The action of astringents may be local or remote. In the former case 

 they are brought directly into contact with the part, as in the case of 

 gargles, injections, eye-washes, &c. In the latter it is necessary that they 

 be first absorbed into the blood, and by it be conveyed to the part to be 

 acted upon. Cold, in the form of ice, evaporating lotions, or freezing- 

 mixtures, is spoken of as an astringent. The mineral acids, and their salts 

 also, if soluble, have a similar effect, particularly the salts of lead, zinc, 

 iron, copper, aluminium, silver, and mercury. Among the chief vegetable 

 astringents used in veterinary medicines may be mentioned gallic and 

 tannic acids, and the bai'ks of trees which have astringing or binding pro- 

 perties due to these or similar constituents. Oak bark and oak-galls are 

 among the most powerful ; white elm bark, catechu, witch-hazel, and others 

 are more or less employed on account of their astringent properties. 



The immediate effect of such agents upon mucous surfaces, and soft 

 parts generally, is to contract them, whilst some also coagulate the alluimen 

 with which they are brought into contact. 



The action upon living tissues is somewhat similar to that of tanning 

 skins, by the formation of a tanno-gelatin. 



Some astringents administered as internal medicines counteract the 

 relaxed condition of mucous surfaces, and some pos.sess the property of 

 arresting hfemorrhaoe. 



Externally applied, remedies of this class arrest excessive secretions 

 and discharges of pus, serum, and mucous or muco-purulent discharges, as, 

 for example, in abscesses, ulcers, and catarrhal diseases of a more or less 

 chronic character. 



Astringents in the more popular acceptation of the term are those 

 remedies usually employed to arrest diarrhoea only, but it will be seen 

 from the foregoing remarks that their uses are very diversified. 



Certain astringents have the jiroperty of causing contraction of the 

 blood-vessels, decreasing the amount of blood circulating in the parts, and 

 so lessening the quantity of secretion given off by it. The mineral acids, 

 sulphuric especially, have this astringent effect. 



