Of the two cases in which it failed, one was the tertian of three months, attended with the eruption; the other was the relapsed tertian of three days.
With regard to the dose, I began with giving it in the quantity of two grains thrice a day, which, in some, produced the desired effect, and without the least sensible operation on the stomach or bowels. If this dose did not stop the fits after a few days trial, it was increased to three grains, which, in some, would produce a little sickness. I found that four grains ruffled the stomach a good deal; but if the patient is gradually habituated to it, even more than this may be given without inconvenience.
In those cases in which it was successful it was not found necessary to give more than two grains at a dose, except in one of them, in which three were given the day before the fit ceased. In the two unsuccessful cases the medicine had a fair trial for a fortnight; but one of them getting no better, and the other seeming to get worse, it was left off.
The cases to which this medicine is adapted are those that have extremely distinct remissions, with no symptoms of bile nor any local affection. When agues come to be long protracted, they are frequently what may be called nervous; that is, consisting of certain morbid motions that seem to be induced by habit, after the original cause is removed, and with a tolerable enjoyment of appetite, sleep, and all the functions of life, during the intermission.
The two cases in which the zinc failed recovered by the use of the bark. This had been unsuccessfully tried before, and its good effects now might either depend on its having been left off for some time, whereby the body recovered its sensibility to its virtues, or it might be in consequence of administering it in ardent spirits with a few grains of capsicum and ginger, additions which I found to improve its effects in other cases, and is a mode of giving it well suited to this climate.
The zinc was not tried in the sixth case, on account of the local affection and the remission being short and imperfect.
The white vitriol, being a salt of zinc, might be supposed to possess the same virtues; and it would appear to do so from some facts[111] that were reported to me in the West Indies, and also from some trials made by me at St. Thomas’s hospital since I came to England.
Though this is a medicine of very considerable powers, I do not mean to put it in competition with the bark, by proposing it as a substitute for it, or by representing it as superior to it in all circumstances; but only to propose it as a valuable subsidiary in particular cases. The account I have given is faithfully extracted from a diary of my practice; and were I to say more in its favour than the future experience of others may warrant, I should do more harm than service to its reputation. Many good medicines have had their characters hurt by being over-rated by the first proposers of them, who are naturally sanguine and partial, without, perhaps, intending to deceive. But when others find that their virtues do not come up to what has been asserted, they are apt to run into the other extreme, and explode them altogether; so that what was given out as good for every thing, is now found to be good for nothing[112].