Citric acid (acidum citricum, H3C6H5O7) occurs in large quantities in fruits of the citrus family, the lemon, orange, lime, and grape-fruit; and in milk to the extent of 0.1-0.25 Per cent.

Tartaric acid (acidum tartaricum, H2C4H4O6) occurs in grapes.

They are both crystalline solids, readily soluble in water. In the duodenum they form sodium citrate and tartrate. These salts and the acids are not readily absorbed, and have a laxative effect in the intestine. The alkaline salts are changed to carbonate in the blood, and so serve as systemic alkalinizers. Lemonade and Imperial drink are refreshing drinks in fever. The latter is made by dissolving 1 drams (6-gm.) of potassium bitartrate (cream of tartar) in 2 pints (1 liter) of boiling water, and adding 1/2 ounce (15 gm.) each of sugar and grated fresh lemon-peel. In the duodenum potassium bitartrate, which has an acid reaction, forms Rochelle salt (potassium and sodium tartrate).

When a weak solution of a soluble citrate is mixed with or injected into the blood, it takes up calcium and has a retarding influence upon the clotting of the blood. Because of this action, citric acid has been recommended in the late stages of typhoid fever to prevent thrombosis. But Rudolf and Cole (1911) have determined that citric acid administered by mouth does not essentially influence the time of coagulation of the blood either in typhoid fever or in other conditions; and Addis (1909) has shown that in amounts of 60 to 120 grains (4-8 gm.) a day the drug does not affect coagulability. Janney has administered up to 1 ounce (30 gm.) with sodium bicarbonate without apparent harm.

Formic acid (acidum formicum, Hcooh) has been employed locally and internally in rheumatism. It is present in the secretion of the sting of the bee, and has been employed by allowing bees to sting the involved part.

Acetic acid (acidum aceticum, Ch3cooh) is the essential ingredient of vinegar. The Pharmacopoeia recognizes glacial acetic acid of 99 per cent. strength, which is used for the removal of warts; acetic acid, of 36 per cent. strength; and diluted acetic acid, of 6 per cent. strength. The last is of the strength of good vinegar. A 2 per cent. solution is also employed as an intrauterine hemostatic in postpartum hemorrhage. Trichloracetic acid, CCl3Cooh, is strongly caustic, and is employed in the removal of warts, small nevi, and hypertrophied tissue, such as occurs in the nose. The acetates are freely soluble in water, are readily absorbed, and by changing to carbonate act as agents to alkalinize the blood. They are diuretic, and their intravenous administration is followed by a fall in arterial pressure, and dilatation of the kidney arterioles.

Lactic acid (acidum lacticum, C3H6O3), obtained by fermentation from sugar-of-milk, finds its chief use in 10 to 50 per cent. solution in glycerin as an application to tuberculous ulcers of the throat.

Recently, on the theory that putrefactive germs in the intestines are inhibited by lactic acid germs and their products, the lactic acid drinks have come into extensive use both by physicians and the laity. Such drinks are: zoolak, fermillac, kumyss, sour milk, buttermilk, etc. Special strains of lactic-acid bacteria are also sold to be used in making sour milk, or to be swallowed in the form of capsules, tablets, or liquids. In the opinion of Herter, Bryce, Mendel, the author, and others this form of medication has no real value, many researches indicating little if any use for the drinks except for their nutritive constituents. Lactic acid drinks are prone to induce attacks of gastric hyperacidity, and to bring on rheumatic manifestations in those subject to rheumatism. A recent claim that they are of value in diabetes requires extensive clinical testing.

Oxalic acid (H2C2O4) has no use in therapeutics, but is of interest because of the frequency of its poisoning. This usually occurs from the drinking of solutions used in the kitchen for brightening copper boilers. The crystals resemble somewhat those of Epsom salts. There are - (1) Severe irritation of the gastro-intestinal tract, with vomiting, diarrhea, and cramps, and (2) nervous manifestations, from twitching of the muscles to complete tetany (continuous cramps of voluntary muscles), and convulsions, coma, and death. When death does not ensue, there may be a remote local effect upon the kidneys resulting in nephritis. The systemic symptoms are those of acidosis, or of the removal from the system of calcium, for which oxalic acid has a great affinity.

The chemic antidote for the stomach is a calcium salt, such as lime or the chloride or lactate, to form the insoluble and non-corrosive calcium oxalate. Even wall-plaster may serve if there is no lime at hand. For the systemic symptoms the need is to alkalinize and to supply calcium; therefore a pint (500 c.c.) of a solution of 0.25 per cent. of calcium chloride with 1 per cent. of sodium bicarbonate may be administered intravenously. Copious drafts of water should be given by mouth to promote the elimination of oxalate by the kidneys.