ACTION OF ACIDS 269 



the other mineral salts. Nitric acid is less caustic, and 

 hydrochloric acid is the least corrosive. Nitric acid stains 

 the parts yellow, and hydrochloric, white. The vegetable 

 acids, as citric and tartaric acids, are slightly caustic, but 

 are irritant to the skin, and still more so to raw surfaces and 

 mucous membranes. An ounce of tartaric acid has caused 

 death in man through its local effect. The action of the 

 caustic alkalies is more widespread than that of the mineral 

 acids. Diluted sulphuric and nitric acids are astringents, 

 because of their power of condensing tissues, and also 

 hemostatics in causing compression of blood vessels by 

 contraction of the tissues about them. Nitric acid is com- 

 monly employed externally, because its effect is limited by 

 its own eschar, which is not dissolved by an excess of acid. 



Hydrochloric acid has no astringent effect and is not 

 used externally for its caustic properties. The acids are 

 antiseptic, but are less appropriate than other agents in most 

 cases, on account of their irritant action. Free hydro- 

 chloric acid as it exists in the gastric juice (0.2-0.3 of 1 per 

 cent.) is a powerful antiseptic and even germicide. 



Action Internal. — Alimentary Canal. — The classical ex- 

 periments of Pawlow have materially altered our concep- 

 tions of the action of acids. We have shown (p. 18) that 

 indirectly, by stimulating the formation of secretin in the 

 stomach and intestines, they excite the activity of all 

 the glands giving rise to the secretions concerned with di- 

 gestive activity. They all aid digestion. Hydrochloric acid 

 is particularly serviceable in gastric anacidity, being the 

 natural acid of the gastric juice. The mineral acids also 

 possess a certain degree of antiseptic action on the contents of 

 the digestive tract. Diluted acids are called refrigerants in 

 imparting a sense of coolness to the skin and mucous mem- 

 brane of the mouth, and, by augmenting the secretion of 

 saliva, relieve thirst in fever. The acids exert a local stimu- 

 lant and astringent action upon the intestinal canal. Nitric 

 acid is particularly a stimulant, sulphuric acid an astringent. 



Constitutional Action. — Almost all living matter poss- 

 esses an alkaline or neutral reaction. An animal dies from 

 acid poisoning even before its blood becomes neutral. The 

 constitutional action of acids is seen after absorption of di- 



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