328 MINERAL ACIDS 



present. In this way they are serviceable not only in 

 indigestion, but in certain cases of diarrhoea. 



Before reaching the general circulation, acids must pass 

 through the liver, where they alter processes of tissue change, 

 and check formation of urea (Brunton). As hepatic tonics 

 and stimulants, nitric and nitro-hydrochloric acids are 

 preferred. 



When they enter the blood, their acidity has been neutral- 

 ised, and they are present as salts. The blood is made less 

 alkaline, but cannot become acid during life or it would cease 

 to be able to carry the carbon dioxide from the tissues. 

 To prevent this dangerous acid intoxication in carnivora, 

 the ammonia liberated from the tissues as a result of the 

 breaking down of proteid food combines with the acid in 

 the portal vein and the resulting ammonia salts are excreted 

 in the urine. In herbivora there is little available ammonia 

 but more potassium and sodium in the blood, and so these 

 fixed alkalies have to combine with the dangerous acid and 

 are excreted in the form of salts in the urine, causing some 

 amount of diuresis. Thus acids reduce the alkalinity of 

 the blood more seriously in herbivora than in carnivora and 

 man. They are excreted from the body in part through 

 the intestinal mucous membrane, but chiefly by the kidneys 

 in combination with ammonia and other bases. Full or 

 repeated doses diminish, however, the alkalinity, or increase 

 the normal acidity of the urine, by the presence in it of acid 

 salts, and these cause some irritation in the urinary passages. 

 Acetic, citric, and tartaric acids, being readily oxidised into 

 carbonates, exert a primary acid, but a secondary alkaline 

 effect, notably on the urine. 



On account of their astringent effect on the gastric 

 mucous membrane, acids should not be prescribed for more 

 than a week or ten days at a time. They must be given 

 freely diluted, and are often conjoined with bitters, iron 

 salts, and alcoholic stimulants. 



The several acids, although possessing properties in 

 common, have distinguishing characteristics. Hydrochloric 

 being volatile, and possessing, whether in the gaseous or 

 fluid state, a strong affinity for water, is most destructive to 

 vegetation, browning and shrivelling plant tissues. Nitro- 



