456

ELEMENTS OF MATERIA MEDICA.

Physiological Effects. —In full doses (as fifteen grains) it frequentlyacts as a purgative. In small doses it is alterative, and, by repetition,produces the before-mentioned constitutional effects of mercurials.

Uses. —The practice of giving a blue pill at night, and a sennadraught the following morning, has become somewhat popular, in con-sequence of its being recommended by the late Mr. Abemcthy, in variousdisorders of the chylopoietic viscera. As an alterative, in doses of twoor three grains, blue pill is frequently resorted to. Lastly, it is one of thebest internal agents for exciting salivation, in the various diseases forwhich mercury is adapted.

Administration. —The usual mode of exhibiting it is in the form ofpill, in the doses already mentioned; but it may also be administeredwhen suspended in a thick mucilaginous liquid. If the object be toexcite salivation, we may give five grains in the morning, and from fiveto ten in the evening; and to prevent purging, opium maybe conjoined.

Unguen'tum Hydrar'gtjri. — Oint'ment of Mer'cury,

History. —Mercurial ointment was known to, and employed by, theancient Arabian physicians—for example, Ablienguefith, llhazes, andAvicenna : so that it has been in use certainly 1000 years. However,Gilbertus Anglicus , who lived about the commencement of the thirteenthcentury, was the first who gave a detailed account of the method ofextinguishing mercury by fatty matters. Besides its more commonappellation of mercurial ointment , it was formerly termed blue orNeapolitan ointment.

Preparation. —In the London, Dublin, Edinburgh, and UnitedStates Pharmacopoeias , the unguentum hydrargyri fortius is prepared byrubbing two pounds of mercury with an ounce of suet and twenty-threeounces of lard, until globules are no longer visible. To promote theextinction of the mercury, the metal should be previously triturated withsome old mercurial ointment. Rancid lard also assists the extinction ofthe globules.

Some assert that the mercury is in a finely-divided metallic state,though, if well prepared, there are no appearances of globules when theointment is examined by a lens. In favour of this view Guibourt( Pharm . Raisonnee, ii. 140) states, that by digesting ether on mercurialointment, the fatty matter may be dissolved and liquid mercury obtainedin equal weight to that used in making the ointment. Now it is unlikely,if the mercury had been previously oxidized, that the ether coulddeoxidize it; and therefore, this experiment (supposing the results to bethose mentioned) appears almost decisive that the mercury is in themetallic state; but on repetition of the experiment, I have not obtainedthe results stated by M. Guibourt. Mr. Donovan, however, thinks thatpart of the mercury attracts oxygen, and that the oxide thus formedunites with the fatty matter. I have seen no satisfactory explanation ofthe efficacy of old mercurial ointment in extinguishing the mercury;Guibourt offers the following:—By trituration, both lard and mercuryassume oppositely electrical states, the lard becoming negative, themercury positive; these states, he supposes, determine a more intimatemixture of the particles, and a greater division of the mercurv. Now