The agency of the different menstrua on the red and yellow varieties of the cinchona, produces apparently the same results as on the common or pale bark, varying, however, very considerably in degree ; the red being more powerful than the common, and the yellow still more so than the red.
It is an object of considerable importance, as well as of curiosity, to determine exactly the proportions in which the different principles exist, in the varieties of bark, as well as the relations which these principles have to their efficacy as a medicine; but, unfortunately, the difficulties which are opposed to the analyses of such fleeting and delicate substances, as the principles of vege tables, render this desire unavailing, at least in the pre sent state of science. The greater solidity of the princi ples of bark in hot water and in alcohol, would induce a belief of its being a resin; while, on the other hand, their partial solidity in cold water, and their decomposition even by a moderate degree of heat, are characteristic of the extractive principle.
The effects of chalybeates on the infusions of Peruvian bark, indicate the presence of an astringent matter, which seems to be intimately connected with the substance ex tracted by heated water or by alcohol. The addition of a solution of the sulphate of iron to the infusion, strikes a dark olive green colour; a deeper shade of the same co lour is produced by this salt in the decoction or tincture. From this fact, it has been inferred, that tannin is pre sent, and, consequently, that a precipitate would be pro duced by a solution of gelatine. This effect, however, is only induced in some varieties of the Peruvian bark ; there being others, the infusions of which are not, in the slightest degree, affected by the addition of gelatine, but yield a precipitate on the addition of tannin. These sin gular phenomena have given rise to a very absurd hypo thesis of Seguin, in which he ascribes the agency of Pe ruvian bark to the presence of gelatine.
Dr Duncan ascribes these effects to a new agent, which he calls cinchonin. Vauquelin has made extended expe riments on the different species of cinchona, but they are of less value than they would have been, had he detail ed the specific characters of each. Mr Murray has found, "that the watery infusion the pale bark is not sensibly precipitated either in gelatine or tannin ; that of the red bark is not precipitated by gelatine, but gives a copious precipitate with tannin ; and that of the yellow is rendered turbid by gelatine, and precipitated copious ly by tannin." It is vain to throw out conjectures, as to the nature of this substance, until farther facts be determined, on which we can rest with greater certain ty.
Vauquelin has determined the presence of a peculiar acid, to which he gives the name of kink acid, in some varieties of the bark.
The active principles of bark are rendered more solu ble in water by the acids, the alkalies, and sonic of the earths, more especially magnesia.
'Much diversity of opinion prevails among medical men respecting the relative efficacy of the three kinds of bark which we have enumerated. The red bark, when first introduced into English practice, in Lonsequence of a Spanish vessel, freighted in part with it, being taken in the year 1779, was tried in several of the London hospi tals, and was then, as is usual with every new remedy, extolled to the skies ; but its reputation has given way to that of the yellow bark, which is now generally con sidered to be most efficacious.
The preparations of bark, which are admitted into the British Pharmacopoeias, are, the decoction, the ex tract, the infusion, the tincture, and the compound tinc ture. The powder is unquestionably the most efficaci ous when the patients stomach can bear it ; and the other preparations must be resorted to when its use is inexpe dient. Of these, the extract appeals to be the least cal culated to do any good. The practitioner must be guid
ed, in a great measure, by the habits and delicacy of the patient. Sec MEDICINE.
It is utterly impossible to say in what. manner the Pe ruvian bark acts on the human constitution. In general, it is considered tonic, antiseptic, and astringent, and it may possess all of these qualities in a very pre-eminent de gree ; but still no clue is furnished by them to develope the mode in which it acts in the cure of disease. Thus, for example, every physician is well acquainted with the symptoms of intermittent fever, but there are few suffi ciently daring to arrogate any decided knowledge of the causes of these symptoms ; every practitioner has some hypothesis of his own, but if he be a man of common sense, lie will never make that the basis of his practice. In like manner, experience has shown, that Peruvian bark almost universally cures this fever ; but how this cure is induced, it is impossible to determine, until we are assu red of the nature of the diseased action which it over comes. The effects of bark are very powerful; and it is a very remarkable fact, that its action is imperceptible on the human constitution. The only effects of an over dose, arc headache and nausea. Whatever difference of opinion may prevail respecting the mode in which the Peruvian bark produces its effects, there is no doubt of the very decided character of these effects. In intermit tent fever it was first used, and what is very rare in the history of medicine, still maintains its pre-eminence over every other remedy in general application. Experience too has taught almost the whole host of medical men, that it may be administered very safely in large quanti ties, in all stages of the disease, without any other pre paration than that of previously evacuating the stomach by an emetic, or by a cathartic. It has been supposed most useful when exhibited before the recurrence of the paroxysm. It may be given even in the hot stage, though it is then more liable to induce nausea. But the more common mode of practice is to administer it during the interval of the paroxysm. Frequently very smart at tacks of intermittent fever have been cut short by the timcous use of this medicine. The usual dose is from one to two scruples every MI or sixth hour during the intervals of the paroxysms, and this should be continued for some time (which must be determined by circumstan ces) to prevent a relapse.
In remittent fever, particularly the bilious remittent of hot climates, even where the remission is very obscure, bark may be administered with great freedom, and very generally with much advantage.
It is given in diseases of debility, such as typhus, cy nanchi maligna, in passive hxmorrhagies, confluent small pox, in dysentery. It is also employed in scrofula, ill conditioned ulcers, &c. In the first of these classes it does not appear so beneficial as wine, from the weak state of the organs of digestion. When the patient is convalescent, it is considered more useful.
Bark has been used very freely in rheumatism, particu larly among the London practitioners, and very generally with advantage. It is the object of another article to cuter more fully into the uses of this very valuable re medy.
Half a drachm is the usual dose ; but, under particu lar circumstances, the quantity ma? be very much aug mented. •I'wo ounces have been taken, in urgent cases, in the course of twenty-four hours.
The powder, as before hinted, is the most efficacious form in which it may be administered, either mixed up with water, milk, jelly, or any other simple vellicht, or combined •ita some stimulant aromatic matters. It sometimes excites vomiting and purging, M rich trust be corrected by the usual means. See Thomson's Chemis try. Murray's Materia Medica. Pharmacon.
Land. Edin. &c. Practice of Physic. (passim) Thomas and Cullen See also MEniela:E. (c. at.) CINCINNATUS. See Rona.