1. Metallic Mercury and preparations containing it.

2. The Perchloride of Mercury and its preparations.

3. The Subchloride of Mercury and its preparations.

4. The Oxides, Iodides, the Ammoniated Mercury, and their preparations, a complex group, the action and uses of which closely correspond either with those of the perchloride or with those of the subchloride.

5. Acid Nitrate of Mercury and the Ointment corresponding. 1. Metallic Mercury and its preparations. - These may be employed in all the classes of cases for which mercurials are adapted. The metal itself is never given internally, except in the finely-divided form in which it exists in Pilula Hydrargyri and Hydrargyrum cum Cretâ. The blue pill is chiefly used as a purgative and indirect cholagogue, but is also given in syphilis, in small doses combined with opium and quinine, and in combination with digitalis and scilla as a diuretic (the famous "Guy's pill)." Hydrargyrum cum Cretâ, or "grey powder," is a favourite purgative for children, and also a convenient preparation for a course of mercury in syphilis. Unguentum Hydrargyri, or "blue ointment," is the usual means of administering the metal by inunction in syphilis. A portion as la as a pea or hazel nut is rubbed daily into a soft part of the skin, such as the inside of the thigh, or smeared on flannel, and applied round the loins, the gums being carefully watched. This is a very sure and tolerably safe, but very dirty method, which is chiefly employed with infants. The non-officinal oleate, painted on, is a great improvement in this respect. Mercurial ointment may also be smeared over inflamed parts, such as the testis, and is used as a parasiticide. The Liniment of Mercury (the ointment in a liquid form) is chiefly employed as an antiphlogistic, being soaked on lint and applied to the affected part, e.g. the joints or the abdomen in subacute peritonitis, The same use may be made of the plasters, and of the compound ointment, "Scott's dressing." The suppository may be used in syphilis or to kill ascarides.

2. Perchloride Of Mercury

Perchloride Of Mercury. This is the most powerful of all mercurials. It is one of the most active of antiseptics, being 100 times as strong as carbolic acid, and may he used to disinfect foul ulcers, especially of syphilitic origin, a certain amount of caustic and stimulant effect being secured at the same time. It must he cautiously employed. It is also used to destroy the fungus of ringworm. Internally, as the Liquor (a weak solution), it is given in syphilis only, never as a purgative. In this form, the perchloride is by no means an irritant preparation of mercury, hut rather the reverse. Lotio Hy-drargyri Flava, "yellow wash," containing the yellow oxide, is applied to syphilitic sores.

3. Subchloride Of Mercury

Subchloride Of Mercury. Calomel resembles metallic mercury in being used externally and internally, as a purgative, alterative, and antisyphilitic remedy. Externally it is applied to syphilitic sores and chronic inflammatory growths as calomel dust, by fumigation, as the unguentum, and as the black wash. Internally calomel is a valuable purgative, with the powerful action as an indirect cholagogue and hepatic stimulant already described. The compound calomel pill (Plummer's pill) is in much repute as a hepatic stimulant and alterative, with little or no directly purgative effect, given every night or every other night for a week at a time, in gout and loaded conditions of the system consequent on free living. Calomel, combined with opium, was the favourite mercurial employed by the last generation of surgeons and physicians in the treatment of inflammation, to which wo have already referred. In syphilis the same combination is still employed with success.

4. The Oxides, Iodides, And Ammonio-Chloride Of Mercury

The Oxides, Iodides, And Ammonio-Chloride Of Mercury. These substances, although forming a convenient group, belong, as regard their action and uses, partly to the second and partly to the third group above. Thus the following closely resemble the perchloride, viz. Hydrargyri ( Oxidum Flavum, Hy-drargyri Oxidum Rubrum, Hydrargyri Iodidum Rubrum, and Hydrargyrum Ammoniatum. The first two are almost exclusively used in syphilis, and externally, chiefly according to the opinion and custom of the practitioner. The "white precipitate" ointment is useful as a parasiticide, and as a stimulant application to chronic inflammatory eruptions of almost any kind in children. Along with the subchloride is to be classed Hydrargyri Iodidum Viride, which is much used in syphilis by some surgeons. Donovan's Solution is valuable in obstinate syphilides. The student will not forget that the Lotio Hydrargyri Flava really contains the yellow oxide, and the Lotio Hydrargyri Nigra, the black oxide, although they are reckoned as preparations of the perchloride and subchloride respectively.

5. Liquor Hydrargyri Nitratis Acidus, And The Ointment Of The Nitrate

Liquor Hydrargyri Nitratis Acidus, And The Ointment Of The Nitrate. These are not used in syphilis; but the former is used as a caustic in lupus and other limited growths and ulcers of the skin; while the ointment is of value as a stimulant in cases of chronic skin disease, and is applied to the edges of the eyelids in chronic inflammation and ulceration of the hair follicles.

Precautions in the use of mercurials. - Mercury must not be given as an alterative, antiphlogistic, or antisyphilitic remedy in persons with anaemia or debility, unless these are distinctly referable to syphilis, and even then it must be em-ployed with caution. Tuberculosis and kidney disease also contra-indicate the use of mercury; and certain individuals will ionally be met with in whom even small doses of calomel or blue pill quickly induce hydrargyrism by a kind of idiosyncrasy. In every instance the patient must be carefully nourished, as we have said. On the contrary, children - own infants - bear mercury very well, although the prolonged administration of the metal to them appears to produce a peculiar change in the permanent teeth when they appear, which is extremely unsightly ("mercurial teeth" of Hutchinson).