UNGUENTA. L.E.D. Ointments.
These are unctuous substances analogous to Cerates except in consistence, which is much less firm, and scarcely exceeds that of butter: formerly, ointments were numerous and complicated in their composition, and surgeons adapted with much technical formality different ointments to answer different indications: this practice however has undergone a very judicious reform, and it is now well understood that in general all that is required in an ointment is a suitable tenacity and consistence, to keep the parts to which it may be applied soft and easy, and at the same time to exclude from them the atmospheric air; in some cases, however, these simple compositions are made the vehicles of more active remedies, as in the following preparations, viz.
Unguentum Cantharidis. L. As the active ingredient in this ointment is derived from an infusion of the Cantharides, it is extremely mild, and frequently inefficacious. The ceratum cantharidis furnishes a more certain application.
Unguentum Elemi Compositum. L. The elemi and turpentine in this ointment, render it stimulant and digestive.
Unguentum Hydrargyri Fortius. L. The precise nature[[713]] of this compound does not appear to have been known until the late researches[[714]] of Mr. Donovan, (Annals of Philosophy, November, 1819,) which promise to lead to a more uniform, efficacious, and economical mode of preparing it; for they[[715]] shew that in the officinal ointment, the mercury exists in two different conditions,—in the state of metal, mechanically mixed, as asserted by Vogel, and in that of an oxide, chemically combined with the lard, and that the medicinal activity of the ointment exclusively resides in this latter portion, the presence of metallic mercury not only being useless but injurious, by obstructing the absorption of the active compound of the oxide. Mr. Donovan accordingly formed a direct chemical combination, by continually agitating together lard and black oxide of mercury at the temperature of 350° Fah: for two hours. At the end of the process it appeared that every ounce of lard had dissolved, and combined with 21 grains of oxide; and from the trials which have been made respecting its activity, it would seem to be as efficient as the officinal ointment, and moreover that it may be introduced by inunction in one third of the time. The investigation is highly important, for it not only offers the means of preparing a mercurial ointment more œconomically, but one more active and manageable, and less liable to that want of uniformity in strength, which must always attend a preparation in which so much labour is required for its completion; for independent of that variation in strength which will arise from imperfect triture, it is by no means an uncommon practice to use chemical means, which are not admissible, to facilitate the process, such as the addition of Sulphur, which is found to abridge very considerably the labour requisite for the extinction of the mercury, but it converts a portion of the metal into a Sulphuret, and diminishes the power of the unguent. There is however a method of facilitating the process, which is not liable to any apparent objection, but the theory of its operation is obscure; it consists in adding to the half-prepared ointment a portion of that which has been long kept; which appears to act as a leaven to the whole mass.
The following table exhibits the relative quantity of mercury contained in each of the different ointments directed by the British Pharmacopœia, and in that prepared according to the process of Donovan.
| One Drachm | { | stronger ointment contains of Mercury | 30 grs. | |
| of the Lond: | weaker ointment | 10 —— | ||
| of the Edinb: | common ointment | 12 —— | ||
| of the Dub: | { | stronger ointment | 30 —— | |
| weaker ointment | 20 —— | |||
| of that prepared according to Donovan | 2½ —— | |||
Mercurial ointment furnishes the most prompt, and least exceptionable mode of impregnating the system. The external method of administering mercury, says Mr. John Hunter, is always preferable to the internal, because the skin is not nearly so essential to life as the stomach, and therefore is capable in itself of bearing much more than the stomach. The inunction is generally performed by rubbing ʒss to ʒj on some part of the body where the cuticle is thin, generally on the inside of the thigh, except perhaps in cases of chronic hepatitis, when it is more usually applied to the region of the liver, care being taken that the friction is continued until every particle of the ointment disappears; and for obvious reasons, the operation ought if practicable to be performed by the patient himself. Where it has been an object to saturate the system with mercury as quickly as possible, I have witnessed the advantage of confining, by means of slips of bladder, a drachm of mercurial ointment in each axilla, in addition to the mercurial friction. Camphor, turpentine, and other stimulants, have been sometimes added to the ointment, with a view of promoting its absorption; this however is an erroneous practice, since these acrid ingredients soon produce pustules on the skin, which prevent the continuance of the friction; the warm bath is a more certain, and less objectionable adjuvant, many practitioners therefore advise the body to be immersed in a warm bath, once and again, before the course is commenced, and to repeat it once or twice a week during its continuance: the length of time to be employed in a course of mercury, and the quantity to be given, are circumstances that must in every case be left to the discretion of the practitioner. Mercury, when introduced into the body, acts as a powerful stimulant, and pervades every part of the system; hence it is the most powerful evacuant belonging to the Materia Medica; from its stimulant operation, exerted directly or indirectly, we are able to explain its utility in the cure of disease, and it may be made to act according to management and circumstances, as a tonic, antispasmodic, diuretic, cathartic, sialogogue, emmenagogue, or alterative; but its most important operation is that displayed in removing the diseases induced by the syphilitic poison, although its modus operandi is still buried amongst the many other arcana of physic. The mode of directing and controlling the influence of mercury in the cure of the venereal disease, is now very generally understood, and it is to be hoped that a full confidence in its antisyphilitic powers is as universally maintained, in spite of the late opinions which tended to depreciate its value and to question its necessity; there is however no advantage to be gained, as was once imagined, by exciting profuse salivation. On its next important application, that of curing chronic affections of the liver and dropsy, a remark which has been suggested to me by the results of practice, may not be unacceptable. I think I have generally observed, that when the remedy has been pushed to such an extent as to excite the salivary glands to excessive secretion, the urinary organs cease to participate in its stimulating action, and vice versa, for the mouth is rarely affected when the mercury runs off by the kidneys; this may suggest a precaution of some practical moment in the treatment of dropsy, and it will be generally judicious to accompany the administration of this metal with certain diuretics, in order to direct its operation to the kidneys;[[716]] and it would seem, that for such an object those diuretic medicines should be preferred that act primarily on the organs, as alkalies and their combinations, squill, &c. the success of such a plan of treatment will also depend greatly upon the exact period at which these remedies are administered; it will for instance be right to wait until the system is, to a certain degree, under mercurial influence. It is hardly necessary to observe, that if the mercury runs off by the bowels, we shall be deprived of all, or of a great share of, the benefit to be expected. In certain cases, the lymphatic vessels seem to resist the admittance of mercury, and to refuse the conveyance of it to the general circulation: I have already thrown out some vague hints upon the subject, at page 156, and I must refer the reader to some farther remarks, which I apprehend bear upon this question under the following article.
Unguentum Oxidi Hydrargyri Cinerei. E. This consists of a mixture of one part of grey oxide of mercury, and three parts of axunge: it was reasonable to suppose, a priori, that, as the whole of the mercury in this ointment is oxidized, its adoption would supersede the necessity of the labour required for the preparation of the common mercurial ointment, and at the same time afford a combination of equal if not superior efficacy; but experience has not justified the conclusion, for it has been found to possess little or no activity; the consideration of it is therefore introduced into this work, not on account of its utility, but as an object upon which I may pause with advantage, to offer those observations which its history is so well calculated to call forth and illustrate. The circumstance which renders this preparation inert, will now receive a satisfactory explanation from the experiments of Mr. Donovan, as related in the preceding article; in short, it is a mechanical mixture instead of a chemical combination; and I beg again to urge the importance of this distinction, and to offer the present example as a farther illustration of the views I have already submitted upon the subject. By subjecting this ointment for some hours to a heat of 300°, it would without doubt become an active preparation. It is probable that the lymphatics offers less resistance to the ingress of a mineral body into the system when it is presented to them in combination with some animal substance, which must alone be regarded as their peculiar stimulus, and the only matter which they are destined perpetually to receive and convey; for the same physiological reason, the lacteals may probably take up iron with greater readiness when in combination with vegetable matter, than when introduced into the stomach in a more purely mineral form.
Unguentum Hydrargyri Mitius. L. This weaker preparation is sometimes preferred, as it irritates the skin less; it is however principally used as a topical dressing to venereal sores, and as an application to kill vermin on the body.