There are many official salts and preparations of mercury (hydrargyrum), and their actions and uses are so distinct that they may well be considered separately according to their therapeutic uses. The therapeutic classes are: (1) The disinfectants. (2) The antisyphilitics. (3) The cathartics. (4) Those with special uses.

I. The Disinfectants

(a) Mercuric chloride, hydrargyri chloridum corrosivum, HgCl2, known also as bichloride of mercury or corrosive sublimate, is soluble in 13 parts of water and 3 of alcohol. The U. S. Pharmacopoeia has introduced a bichloride tablet, Toxitabella hydrargyri chloridi corrosivi, which contains mercuric chloride about 7 1/2 grains (0.45-0.55 gm.) and an equal amount of sodium chloride. It must be of angular shape (not discoid), must bear the word "poison" and skull and cross-bones, and must be colored blue, preferably with sodium indigotindisulphonate.

The solution in water takes place slowly, but is hastened by the addition of some sodium or ammonium chloride. These chlorides, however, prevent the ready dissociation of the bichloride into ions, and reduce the antiseptic power about half (Wolf). In Paul and Krony's experiments the number of anthrax colonies obtained after six minutes' exposure of the spores to bichloride, 1: 60, was 8, while when the bichloride was mixed with an equal amount of sodium chloride, they obtained 32 colonies, and with four times as much sodium chloride, 382 colonies. These chlorides retard correspondingly the precipitation of albumin. Mercuric chloride has many incompatibles, such as alkaloids, alkalies, lime-water, and soap. A large basin of bichloride antiseptic solution will be destroyed by a very small amount of green soap. It is also decomposed by carbonates, silicates, and sulphates, such as occur in the natural waters; so that in making its solutions, distilled water is preferable.

A solution of 1: 1,000,000 will kill protozoa, a solution of 1: 10,000 will prevent the growth of molds and bacteria. It takes some time for their destruction, however, and it is absurd to suppose an instrument or the hands to be sterilized by a momentary dipping or rinsing of them in the solution. The spores of bacteria are much more resistant than the germs themselves. The bichloride acts by forming a chemical precipitate with the proteins of the protoplasm; as a consequence, it has little penetrating power and is quickly rendered practically useless by albuminous fluids. It may coagulate an albuminous envelope about bacteria without killing them.

Fig. 64.

Fig. 64. - Destruction of tubular epithelium caused by poisoning with mercury bichloride (MacCallum).

Locally, its solutions are astringent and irritating, and, if strong, are corrosive to the tissues. Even very weak solutions, if much used, cause roughening and discoloration of the skin, and in the form of a continuous wet dressing may produce a dermatitis or a pustular rash.

In 1: 4000 to 1: 1000 aqueous solution mercuric chloride has been one of the most used antiseptics for the hands of the surgeon or obstetrician, for the skin preliminary to operation, for infected wounds, for excreta, and in 1:10,000 solution as an irrigation in any accessible body cavity, as throat, vagina, uterus, bladder, etc. It is also used in fungus and bacterial skin diseases and for pubic lice.

Harrington's solution, as used at the Mayo Clinic, is mercuric chloride, 0.8 gm.; hydrochloric acid, 60 gm.; distilled water, 300 gm.; alcohol, 640 gm.; i. e., 1: 1250 by weight.

(b) The other mercurial antiseptics are less employed. The ointment of mercury in two strengths, viz., mercurial ointment (unguentum hydrargyri), 50 per cent., and blue ointment (un-guentum hydrargyri dilutum), 33 per cent., and the ointment of ammoniated mercury (white precipitate ointment) are employed in fungous and bacterial skin diseases; the ointment of the nitrate of mercury (citrine ointment) is used expecially for ring-worm. The ointment of the yellow oxide is preferred about the eye, as in blepharitis, conjunctivitis, and keratitis.

Schamberg, Kolmer, and Raiziss (1917) have brought forward mercurophen (sodium oxymercury orthonitrophenolate) as a salt which, against Staphylococcus aureus, has in aqueous solution 50 times the disinfectant power of bichloride, and in ascitic fluid 200 times the power of bichloride.

II. The Antisyphilitics

As local applications to venereal sores, mercuric chloride, calomel, and the ointments of mercury and ammoniated mercury are employed. Mercurial ointment (unguentum hydrargyri) contains 50 per cent., and the diluted mercurial ointment (unguentum hydrargyri dilutum), 30 per cent. of mercury. Black wash (lotto nigra, N. F.) is calomel, 4 grains (0.25 gm.), to lime-water, 1 ounce (30 c.c.); yellow wash (lotio flava, N. F.) is bichloride, 1 1/2 grain (0.09 gm.), to lime-water, 1 ounce (30 c.c.).

For the systemic action mercury is administered by inunction, by mouth, and by hypodermatic or intravenous injection. For inunction the mercurial ointment is regularly employed, but it is dirty and tends to irritate the skin, and its absorption is uncertain. Ten to 30 grains are rubbed well into the softer parts of the skin every day or two, a new area being chosen for each successive inunction, on account of irritation. The favorite sites are the inner surfaces of the thighs and arms, and the chest, back, and abdomen. Oleate of mercury and white precipitate ointment are occasionally used instead of mercurial ointment. Weil and Elliott have shown that the mercury, ammoniated mercury (white precipitate), and calomel ointments will mercurialize a patient more readily than an ointment made from the nonvolatile salts such as the salicylate and the oxides.

By mouth, the favorites are the biniodide, 1/16 grain (0.004 gm.), and the protoiodide, 1/4 grain (0.015 gm.), and for children the mercury with chalk, 1 grain (0.06 gm.). The bichloride, dose, 1/32 grain (0.002 gm,), is sometimes given in a mixture with potassium iodide, with which, however, it changes to the biniodide.