The modes of employing mercury, both for its alterative effects on the digestive organs, and its operation on the system, have been already detailed, in connection with the accounts of its several therapeutic applications. it may not be amiss to present them in one view, at the expense of a little repetition.

1. For its alterative influence upon the hepatic or digestive function the medicine is to be kept within the point of salivation. Either the mild chloride (calomel), the mercurial pill (blue mass), or mercury with chalk may be used; the two former being preferable for adults, the latter sometimes for children, especially when there is excess of acid in the stomach and bowels. When there is a disposition to constipation, the most convenient method is to administer a dose every night or every other night, and to follow it in the morning by a gentle laxative, as one or two drachms of Epsom or Rochelle salt. Sometimes it may be advisable to give the mercurial and the laxative together at bedtime, in which case, rhubarb, or aloes, or the two combined may be employed. From half a grain to two grains of calomel, or from two to six grains of the blue mass may be given, according to the degree of effect desired, and the less or greater susceptibility of the patient. For children, as they are in general extremely insusceptible to the sialagogue operation of mercury, it is not necessary to reduce the dose in the same proportion as with ordinary medicines. A grain or two of the blue mass, or one-quarter to half a grain of calomel may be given to a child a year or two old; but special care should be taken that the bowels are opened next morning; and, for this purpose, castor oil or magnesia is preferable to one of the salts.

When the stomach and bowels are irritable, in other words, in cases of cholera or diarrhoea, it is better to give the medicine in smaller doses frequently repeated. One-sixth of a grain of calomel, or half a grain of the blue mass, may be given every hour or two hours, until the quantity amounts to one or two grains of the former, or from three to six grains of the latter for the day; and it will often be desirable, in order to avoid salivation, to administer the medicine only every other day. in very irritable states of the alimentary canal, even smaller doses than those mentioned may be given with propriety. When the patient is extremely susceptible of salivation, very minute quantities will often have the effect; and for such a person the amount should be reduced to one-half or even one-quarter. For a child a year or two old, one-twelfth of a grain of calomel, a quarter of a grain of blue mass, or a grain of the mercury with chalk may be given every hour or two, through the day, and omitted at night. Unless in urgent cases, it will be best with children also to employ the medicine only upon alternate days, using other measures in the intervening days.

I do not think that any advantage will accrue, for the purpose here referred to, from the external use of mercury.

2. With a view to salivation, the medicine may be used by the stomach, by the rectum, externally, and by inhalation. In the great majority of cases, the internal use of the medicine is amply sufficient; and it is very rarely, except in syphilitic affections, that any other method of application is at all necessary or desirable. I would here again impress on the student and young practitioner the importance of being very guarded in this use of mercury, and watchful against too great an effect on the mouth. It is in general quite sufficient that the slightest observable fetor of the breath, increased flow of saliva, or effect on the gums should be produced; after which, the medicine should be so given as only to keep up this effect. This can be readily done in chronic cases. In the acute, especially those of rapid progress, it is often necessary to run the risk of a greater amount of ptyalism; though, even in these, a little caution will generally be sufficient to prevent any inconvenient soreness of the gums.

In chronic cases, from half a grain to a grain of calomel, and from two to five grains of blue mass may be given three times a day; and, in two or three days, gradually increased if the medicine shall have produced no effect. In the acute, the same dose may be given, but more frequently repeated; the interval varying from one to three or four hours, according to circumstances, so that the whole quantity given in twenty-four hours may fall between the extremes of four and twenty-four grains of calomel, and twelve grains and a drachm of the blue mass. The smaller quantity should always be used at first, when there is no urgency, and increased as circumstances may seem to require. It is only in the most rapid and dangerous diseases, that the larger quantity mentioned should be given, or even approached; and, in these cases, calomel should generally be preferred; so that it is very seldom desirable to administer more than twelve or eighteen grains of the blue mass in twenty-four hours. When these doses purge, they should be combined with opium, if not contraindicated. Happily, there is very frequently a coincident indication for the two medicines, in which case they should be given together; and both may often be usefully associated with ipecacuanha.

Should the doses mentioned prove irritant to the bowels, as will sometimes happen even when opium is administered at the same time, a good plan is to exhibit them in extremely minute doses, at proportionably short intervals. Thus, one-twelfth, eighteenth, or even twenty-fourth of a grain of calomel, may be given every half hour till the system is affected; and it will generally be found that a much smaller amount in the aggregate, given in this way, will affect the system, than in larger doses.

Formerly it was not uncommon to give large doses of calomel at once, with a view to salivation; its tendency to act on the bowels being restrained by opium. Five, ten, fifteen grains have thus been given, and sometimes even much larger quantities. But, as only a certain amount of the medicine is dissolved and absorbed within a certain time, the method is not more effectual than that of small doses frequently repeated; and, indeed, often less so, on account of the tendency to purge in these doses, not unfrequently even when combined with opium. But the greatest objection to the plan is, that it places the medicine unnecessarily beyond our control; and, in cases of peculiar susceptibility, very serious effects may ensue.

Corrosive sublimate is sometimes used internally with a view to affect the system; and by some it has been recommended as preferable to the other preparations, from its solubility and consequently greater uniformity of effect; but I have seldom used it except in syphilitic or syphiloid affections, and am not able to speak of it with confidence. More will be said of it among the preparations.*

By Enema. it is possible, sometimes, when the stomach is extremely irritable, or mercury from some other cause cannot be given by the mouth, that advantage may accrue from its exhibition in the form of enema; though practically I have seldom found occasion to resort to this method of administration. The blue mass should be preferably used, as the mildest preparation. it should be rubbed up thoroughly with some mucilaginous fluid, and given with an opiate. The dose may be three times that given by the mouth, and the quantity of liquid vehicle vary from two to four fluidounces.

External Use

When mercury cannot be given, or will not operate by the mouth, or when, from the urgency of the case, it is desirable to introduce the medicine into the system by every avenue, or, finally, when it is thought proper to give it a certain direction, as through diseased lymphatic glands, for example, recourse may be had to its external application, with a view to the production of mercurialism. For this purpose, the officinal mercurial ointment may be used; one drachm of it being rubbed daily, or twice a day, upon the inside of the thighs and legs, or of the arms and forearms. These positions are selected because the skin is there more delicate, and the epidermis is more readily permeable. it has been thought, too, that the number of superficial absorbents might still further favour the absorption of the medicine; and that a direction might thus be given to it through the glands in the groin and axilla.

* Some interesting practical observations in reference to the influence of acid substances, taken simultaneously with the insoluble preparations of mercury, in increasing their tendency to salivate, have been communicated by Dr. Humphrey Peake, of Arkadelphia, Arkansas, to the New Orleans Med. and Surg. Journ. for Nov. 1858, p. 725. He has known the use of cider and buttermilk very much to facilitate this action of mercury; and, therefore, these, as well as all other sour articles of food or drink, should be avoided when calomel is administered as a purgative; while, on the contrary, they may be recommended when a speedy salivation is deemed advisable. (Note to the second edition.)

Another method of applying the ointment is as a dressing to blistered surfaces, deprived of the cuticle. it may be used in this way in all cases of urgency, in which a blister has been produced with other intentions, and a surface fit for the purpose has thus been incidentally obtained. it would rarely be justifiable to make a blister for this special object.

The rubbing of calomel or black oxide of mercury upon the inside of the lips, the gums, etc., has also been recommended in reference to the constitutional impression. Two or three grains are used at once. I have not employed this method; but cannot help suspecting that it is only another mode of exhibiting the medicine by the stomach; as I presume that what is rubbed upon the gums will be much more likely to be swallowed than absorbed from the mouth, even when care may be taken to avoid such a result.

Fumigation is still another method. The mercurials, at an elevated temperature, generally rise readily in vapours, which, either inhaled, or applied to the surface, are capable of bringing the system under the influence of the medicine. When inhaled, the vapour operates more rapidly than any other form in which mercury is used, and has, therefore, been recommended in cases in which a very speedy effect is required; the impression being afterwards sustained by the internal use of the medicine. it is also sometimes applied locally to ulcerated surfaces, in order to change the nature of their action. Personally, however, I have never met with cases in which this mode of using mercury seemed to me to be desirable. Violent effects are said sometimes to have resulted from the inhalation of the vapour; and a great objection to the process is the difficulty of regulating the dose, so as to have the medicine under command. More will be said of it when the individual preparations are treated of, which are used in this way. Cinnabar, the black oxide, and calomel have been employed.