UNG

system is, to a certain degree, under mercurial influence. It is hardlynecessary to observe, that if the mercury runs off by the bowels, we shaifbe deprived of all, or of a great share of, the benefit (o be expected. Incertain cases, the lymphatic vessels seem to resist the admittance of mer-cury, and to refuse the conveyance of it to the general circulation : Ihave already thrown out some vague hints upon the subject, in the firstpart of this work (p. 160), and I must refer the reader to some fartherremarks, which 1 apprehend bear upon this question under the follow-ing article.

Unguentum Oxidi Hydrargyri Cinerei. E. This consists of a mix-ture of one part of grey oxide of mercury, and three parts of axunge : itwas reasonable to suppose, a priori, that, as the whole of the mercury inthis ointment is oxidized, its adoption would supersede the necessity ofthe labour required for the preparation of the common mercurial oint-ment, and at the same time afford a combination of equal if not superiorefficacy ; but experience has not justified the conclusion, for it has beenfound to possess little or no activity ; the consideration of it is thereforeintroduced into this work, not on account of its utility, but as an objectupon which I may pause with advantage, to offer those observationswhich its history is so well calculated to call forth and illustrate. Thecircumstance which renders this preparation inert, will now receive asatisfactory explanation from the experiments of Mr. Donovan, as relat-ed in the preceding article ; in short it is a mechanical mixture, instead ofa chemical combination ; and I beg again to urge the importance of thisdistinction, and to offer the present example as a farther illustration of theviews I have already submitted upon the subject. By subjecting thisointment for some hours to a heat of 300 , it would without doubt becomean active preparation- It is probable that the lymphatics offer less re-sistance to the ingress of a mineral body into the system when it is pre-sented to them in combination with some animal substance, which mustalone be regarded as their peculiar stimulus, and tlie only matter whichthey are destined perpetually to receive and convey; for the same phy-siological reason, the lacteals may probably take up iron with greaterreadiness when in combination wdh vegetable matter, than when intro-duced into the stomach in the more purely mineral form.

Unguentum Hydhargyri Mitius. L. This weaker preparation issometimes preferred as it irritates the skin less ; it is however princi-pally used as a topical dressing t4 venereal sores, and as an application \okill vermin on the body.

Unguentum Hydrargyri Nitratis. L.E.D. vulgo Citrine OintmentIt is stimulant, detergent, and alterative ; when diluted with an equa.quantity of simple ointment or almond oil, it may be almost regarded asspecific in ophthalmia tarsi, smeared upon the cilia every night at bed^-time.

Unguentum Hydrargyri Nitrico-oxydi. L. An excellent stimu-lant application, well adapted for giving energy to indolent ulcers. Ifmixed with any ointment containing resin, it loses its red colour, passingthrough olive green to black, which depends upon the conversion of thered into the black oxide of mercury.

Unguentum Hydrargyri PhiEciPiTATi Albi. L. Stimulant and deter-gent It is said to be very efficacious in certain inveterate forms of the