The various methods of administering mercury locally must here be noticed.

(1) In the form of the ointment, metallic mercury may be applied by inunction, i.e. rubbed into a soft part of the skin. Thus applied, mercury undoubtedly enters the blood; but it has been contended that the metal is not admitted by the skin, but through the lungs, in the form of the vapour arising from the heated body smeared with the ointment, or even in small particles by the mouth. Fortunately, the question is of no practical importance, the fact remaining that the system can be quickly brought under the influence of mercury by inunction. The non-officinal oleate painted on the skin quickly conveys the metal into the system.

(2) The subchloride (calomel) may be administered by fumigation. The vapour of calomel, rising from a vessel heated by a lamp, is conducted to a part or to the whole of the surface of the body of the patient, and there allowed to settle as a fine deposit of the salt. The effect is increased by simultaneous diaphoresis, induced either by the vapour of water or by such a drug as jaborandi. 20 gr. of calomel may thus be fumigated, during a sitting of twenty minutes. The same doubt exists as to the precise way in which the calomel thus applied enters the blood.

(3) As a bath of dilute solutions of the perchloride, say 3 dr. to 30 gallons of water, with 1 dr. of hydrochloric acid.

(4) Mercurials may be dusted on to the raw surface of a blistered portion of the skin, or soft syphilitic growths (condylomata) - the endermic method, when it is rapidly absorbed.

(5) Solutions of the perchloride (albuminates or peptonates) may be injected hypodermically - a powerful method, but apt to produce sores.

(6) The vapour of mercurials may be inhaled, as we have seen; but this method is rarely employed intentionally.

(7) Mercury may be given per rectum, as the officinal suppositories.

The action of mercury admitted to a part of the body by any of these channels is usually more than local, the specific effects of the drug, presently to be described, being shortly developed. At the same time, the local effect will be more marked: skin diseases will be healed, condylomata removed, and indurations and chronic inflammatory processes reduced in connection with the bones or joints.

Internally. - The local action of mercury is the same as externally, according to the nature and strength of the preparation employed. Very dilute solutions of the perchloride (4 gr. to 10 fl.oz., with 8 min. of hydrochloric acid) may be used as a gargle or wash for syphilitic ulcers of the tongue and gums. All the salts of mercury act upon the mouth, gums, and salivary glands, causing salivation; but this effect is due to their excre-tion, not to their immediate influence on the parts, and will be described later.

In the stomach, mercurials combine with the chloride of sodium of the secretions, and, whatever their original form, are converted into a double 6hloride of sodium and mercury, which further unites with the albuminous juices, to form a complex molecule of mercury, sodium, chlorine, and albumen. This compound, although precipitated at first, is soluble in an excess either of chloride of sodium or of albumen; exists in the stomach, therefore, in solution; and is readily diffusible and easily absorbed. It is not specially irritant in moderate quantities, and none of the salts of mercury given in medicinal doses produce vomiting like zinc and copper; indeed, Dr. Ringer has shown that calomel in 1/12-gr. doses, or Hydrargyrum cum Cretâ in 1/3-gr. doses, given every two or three hours, arrests some forms of vomiting in children. In large or concentrated doses, however, mercurials are irritant or corrosive to the stomach, and must be given with caution, after meals.

The irritant effect of mercurials continues in the duodenum, naturally taking the form of purgation. The perchloride is never employed to produce this effect, but divided mercury in the form of the Pilula Hydrargyri and Hydrargyrum cum Creta. and Calomel, are common purgatives. The action of mercurials as purgatives is a purely local one, none of the metal being absorbed, but the whole expelled in the faeces. The exact nature of this action is, however, obscure. Probably the intestinal glands are chiefly stimulated to increased secretion, and the mucous membrane irritated to such a degree as to produce a moderate increase of watery exudation from its vessels into the bowel, peristalsis becoming more brisk at the same time. The result is a thorough evacuation of the contents of the small intestine as a large, loose, but not watery, stool, charged with bile, which has been hurried out directly from the duodenum, and not allowed to re-enter the portal circulation by absorption from the lower bowel, as it normally does. Thus mercurials, especially calomel, increase the amount of bile evacuated without increasing the amount secreted; that is, are indirect cholagogues by being duodenal purgatives. The manner in which indirect cholagogue action stimulates the liver to further secretion is discussed in Part III. The purgative action of mercurials is greatly assisted by a subsequent saline, such as Seidlitz powder, or the Mistura Sennas Composita. The class of diseases in which mercurials are selected as purgatives chiefly include cases of congestion of the portal system and liver, especially those referable to secondary indigestion from free living or gout; cases of constipation attended by irritable stomach, or actual ulceration of the stomach or bowels; very rarely cases of habitual constipation, except at long intervals, to enable gentle laxative measures to act more freely; and occasionally diarrhoea, when it is distinctly referable to biliary derangement, or the presence of an irritant in the bowel, as in children.

2. Action On The Blood And Its Uses

As we have seen, mercury enters the blood freely through the broken or unbroken skin. From the bowel but a small part of a medicinal dose is absorbed, the rest passing off in the faeces as the sulphide, unless combined with opium, which delays its progress through the intestine. The complex molecule which mercury forms in the stomach and intestines is decomposed on entering the blood by combination with oxygen and albumen, an oxyalbuminate of mercury being the result, and apparently the same compound is formed when the metal enters by other channels.