External

Antiseptic action. - Solutions of the corrosive chloride are very largely employed. A strength of 1 in 1000 is used for washing the hands, for washing the parts to be operated upon, for soaking towels, lint, sponges, etc., used in operations, for washing infected articles, infected rooms, furniture, linen, etc. For wounds and cavities (as the uterus), the strength for a single washing should not exceed 1 in 2000, and weaker solutions are preferable; for continual irrigation 1 in 10,000. Corrosive sublimate tablets, tinted blue, made so that one dissolved in a pint of water makes a solution of 1 to 500, are a convenient form in which to carry the antiseptic. Corrosive sublimate solutions should always be tinted blue to render them easy to recognize. The mixed mercury and zinc cyanide as suggested by Lister is unirritating. It is said to have but slight germicidal value, but its inhibitory power is so great that a solution of 1 to 1200 will permanently prevent putrefaction in animal fluids. Cyanide gauze may be made actively germicidal by impregnation with a solution of 1 to 4000 of corrosive mercuric chloride.

Antiparasitic Action

White precipitate ointment, diluted mercuric nitrate ointment, and a wash of corrosive chloride are very useful for destroying lice on the head; and these three, especially the last, are excellent for destroying the fungus in ringworm and favus. The oleate of mercury is useful for destroying that in pityriasis versicolor; if the skin is easily irritated the ointment of it should be used. Mercurials should not be applied over so large an area that there is a risk of poisoning from absorption.

Irritant Action

The acid solution of the nitrate is used to destroy warts, condylomata, etc.; no doubt much of its caustic action is due to the free nitric acid it contains. Milder prepara tions, such as the ointment of mercuric nitrate, or of red mercuric oxide, if diluted, may be used for tinea tarsi; and the same ointments are very beneficial to any ulcer or sore that requires a stimulant, whether or not it be syphilitic. In ophthalmic practice the ointment of yellow mercuric oxide, known as Pagenstecher's ointment or ophthalmic salve, is largely employed. When a milder preparation is required, calomel is often dusted on the part; and black wash Lotio Hydrargyri Nigra, B. P. - Calomel, 1; glycerin, 8; mucilage of tragacanth, 20; lime water, to 160; is very commonly used, especially for syphilitic sores and condylomata. This reaction may be used to determine whether the corrosive mercuric chloride with which gauze has been impregnated has partially changed into the mild chloride. If a black color appears upon application of lime water, calomel is present.

Itching

Black wash, yellow wash Lotio Hydrargyri Flava {see p. 211), or Unguentum Hydrargyri may be employed to relieve the itching of skin diseases, such as pruritus senilis and urticaria, if they are not too extensive. A very favorite ointment for many skin diseases is composed of equal parts of diluted mercuric nitrate, zinc oxide and lead acetate ointments {see p. 178).