This section is from the book "A Treatise On Therapeutics, And Pharmacology Or Materia Medica Vol2", by George B. Wood. Also available from Amazon: Part 1 and Part 2.
Mercurial ointment is prepared by rubbing together equal weights of mercury and fat, the latter consisting of equal weights of lard and suet. The trituration is to be continued until the globules disappear. A portion of the ointment, rubbed upon paper, should exhibit no globules under an ordinary magnifying glass of four powers. Substances are sometimes added, or substituted for the lard, which have the property of facilitating the extinguishment of the mercury; but care should be taken that nothing irritant to the skin is employed, not even rancid lard, as blandness is one of the important requisites of the preparation. So much labour is required for the thorough extinguishment of the metal, that the process is most conveniently conducted by machinery.
The ointment is of a bluish colour, which darkens with age. Though consisting mainly of the comminuted metal and fatty matter, it always contains a small proportion of oxide, which increases with time. Like the other preparations similarly made, however, it probably owes its efficiency to the slow conversion of the metal, by contact with the fluids beneath the cuticle, into a compound soluble in the blood.
When rubbed upon the skin, or applied to blistered surfaces, it is capable of producing mercurialism, and is not unfrequently employed for this purpose. The circumstances requiring its use, and the method of applying it, have already been sufficiently described. (See page 290.) The chief cautions to be observed in its application are, that the operator should protect himself by wearing a thick leather glove, or otherwise covering the hand, and that irritation of the surface should be as much as possible avoided. Sometimes an eruption is produced, with so much inflammation and soreness, as to render a suspension of the application necessary. Hence the importance of having the ointment properly made. As it is also not unfrequently used as a dressing for blistered surfaces, with a view to its effects on the system, and as inflammation of the blistered surface would not only be uncomfortable to the patient, but might counteract absorption, another reason is offered for having the ointment as bland as possible. When it is applied by friction, the rubbing should be continued till the ointment has been absorbed. in chronic cases, a drachm of it may be used morning and evening until the desired effect is obtained; in more urgent cases, the application may be repeated several times a day.
The ointment is often also used for local effect. in venereal buboes and other obstinate glandular swellings, and in tumours of any kind not in their nature incurable, it may be rubbed upon the part affected, or upon other parts from which absorbents may pass into the diseased gland. As a dressing for syphilitic ulcers, it has sometimes proved useful, and has been employed in some cutaneous affections, especially in psora, and for the destruction of vermin which may infest the skin. For these latter purposes, it should be diluted with twice or three times its weight of lard. Within a few years, it has been employed locally for rendering the smallpox eruption abortive, and the prevention of pitting. For this purpose, it should be applied to the face, on the first appearance of the eruption, spread thickly on patent lint, or on muslin, which may be formed into a sort of mask, and kept closely in contact with the skin, so as to exclude the air. Another mode of using it is first to soften it with heat, then thicken it with starch or other farinaceous substance, and, while in a semifluid state, to apply it to the whole surface by means of a brush. The only material inconvenience is the salivation which it sometimes induces; but, if the authority of Tan Swieten, Huxham, and Boerhaave be allowed weight, this is rather an advantage than an evil; for these celebrated authors sanction the use of mercury in smallpox. it is, however, by no means certain that the mercurial ointment operates in diminishing the variolous eruption, in any other mode than by excluding the air; and the same may be said of its use in erysipelas and chilblains, in which it has been recommended.
On the Continent of Europe, mercurial ointment has been employed internally, with a view to the effects of mercury on the system; and, in the dose of from two to five grains, two or three times a day, it is said to salivate with great facility. it may be given in pill, made by incorporating the ointment with lycopodium, or powdered liquorice root.*
Mercurial Liniment (Linimentum Hydrargyri, Br.) is a mixture of mercurial ointment, liniment of camphor, and solution of ammonia, sometimes used as a stimulating application, to promote absorption in local effusions, and for the discussion of chronic and indolent swellings of the joints, glands, periosteum, etc., whether of syphilitic origin or otherwise. it is said to be more apt to salivate than mercurial ointment, in consequence of the presence of ammonia. One drachm of it may be applied twice a day.
* The effects of the salts of mercury with fatty acids have been investigated by M. Jeannet, who has found that the oleo-stearate, applied to the denuded skin, or to the surface of wounds, produces no irritation, and is not absorbed in notable proportion; and that, taken internally, in quantities sufficient to produce the constitutional impression of mercury, it occasions scarcely an appreciable local disturbance in the stomach and bowels. (Archives Gén., Mai, 1859, p. 626.) - Note to the second edition.