The _Red Bark_ upon analysis was found to contain a double basis, and to
yield both _Cinchonia_ and _Quina_, and, what is still more
extraordinary, the quantity of each exceeded that which is known to
exist in the _grey_ and yellow _barks_.
The latest experiments, however, made on very large quantities of the
bark, have shewn that _Quina_ and _Cinchonia_ exist simultaneously in
all the three species; but the _Cinchonia_ is, relatively to the
_Quina_, in greater quantity in the _grey_ bark; whilst, in the _yellow_
bark, the _Quina_ so predominates, that the presence of the _Cinchonia_
might well have escaped notice when small quantities were operated on.
Having thus furnished a sketch of this curious discovery, we have next
to enquire whether the alkaline bases in question do actually
concentrate all the virtues of the barks in which they reside? M.
Majendie[466] informs us that Pelletier had very early after the
discovery transmitted to him a portion of the new substances for trial,
and that he has unequivocally determined that they do not possess any
deleterious qualities,[467] and are therefore essentially different from
the principles of _Nux vomica_, (_Strychnine_,) Opium, (_Morphia_,) &c.
According to the testimony of Dr. Double, as related in the same
journal, they would seem to possess the medicinal properties of the
cinchona.
In the third number of _Majendie’s Journal_ we receive a report from M.
le docteur Renauldin, of an intermittent cured by the _Sulphate of
Cinchonia_, in doses of six grains.
As the discovery of an alkaline element in Opium led the way to the
detection of salifiable bases in other active vegetables,[468] it has
seemed to me preferable that I should introduce those general
observations which I wish to offer upon the subject of those bodies,
under the history of that narcotic. It is only necessary in this place
to caution the practitioner against the hasty generalizations of the too
sanguine chemist; it has already been observed that those vegetable
remedies, whose value has been established by the sober experience of
ages, consist of different principles of activity, or, at least, owe a
modified power to the compound effect of their several ingredients. (_p.
154, note._)
SOLUBILITY OF THE BARK.[469] Cold water extracts its bitter taste, with
some share of its odour; when assisted by a moderate heat, the infusion
is stronger, but becomes turbid as it cools; the infusion cannot be
kept, even for a short time, without undergoing decomposition, and being
spoiled; wine also extracts the virtues of bark, and is prevented by
this substance from becoming sour, a fact which probably depends upon
the avidity with which some of the principles of bark combine with
oxygen, and which may throw some light upon the cause of its antiseptic
virtues. The colouring matter of wine is precipitated by bark, as it is
by charcoal, in the course of a few days. By decoction the active matter
of cinchona is in a great degree extracted, but if the process be
protracted beyond eight or ten minutes, it undergoes a very important
chemical change, the precise nature of which is not well understood; the
balance of affinities, however, by which the different elements are
united, is evidently overthrown, and a considerable precipitation
ensues; oxygen would also appear to have been absorbed; whether the
_Cinchonia_ becomes insoluble has not yet been ascertained, but
experience has shewn that the general loss of solubility, produced by
such a process, is accompanied with a corresponding loss of medicinal
activity; on which account, the extract is necessarily a very
inefficient preparation; if we attempt to redissolve it, not more than
one half is soluble in water. Vinegar is a less powerful solvent than
water; the active matter of bark is rendered more soluble by the
addition of mineral acids, and by the earths and alkalies; these latter
bodies deepen its colour, and precipitate the _Cinchonia_, for which
reason, when they are employed, the decoction ought not to be filtered;
see _Form. 41, 42_, and note thereon. _Lime water_ has been recommended
as a solvent, and it affords an excellent form for children and
dyspeptic patients; for the same reason we obtain a stronger and perhaps
a more efficient preparation, by triturating it with magnesia, previous
to the process of infusion. Alcohol is a very powerful solvent, but the
great activity of this menstruum so limits its dose that we are
prevented from exhibiting a sufficient quantity of the bark in the form
of tincture; it furnishes however an excellent adjunct to other
preparations.
INCOMPATIBLE SUBSTANCES. Precipitates are produced by the _salts of
iron_, _sulphate of zinc_, _nitrate of silver_, _oxy-muriate of
mercury_, _tartarized antimony_, _solutions of arsenic_, _&c._ Any
considerable portion of a tincture produces also a precipitation, which
sometimes does not immediately take place, and the medicinal value of
the bark is probably not impaired by it. As the infusions of _nut galls_
and some other vegetable astringents precipitate the cinchonia from
bark, it becomes a question how far such liquids are medicinally
compatible; saline additions, as _alum_, _muriate of ammonia_, _&c._
have been frequently proposed, but in many such mixtures decompositions
arise which must deceive us with regard to the expected effects. FORMS
OF EXHIBITION. No form is so efficient as that of powder, a fact which
would seem to argue against the _exclusive_ value of the _Cinchonia_;
even the ligneous fibre which the chemist pronounces to be inert and
useless, may produce its share of benefit by modifying the solubility of
the other ingredients, or by performing some mechanical duty which we
are at present unable to understand or appreciate; but where the stomach
rejects it, it must be administered in _infusion_ or _decoction_, with
the addition of its _tincture_. In cases where it is necessary to join
cordials, an infusion of bark in Port wine[470] is a popular and very
useful form for its administration. DOSE of the powder, gr. v to ʒij or
more, of the infusion or decoction ℥ij. MEDICINAL USES. It is powerfully
tonic and antiseptic; it was introduced into practice for curing
intermittent fevers, but since that period it has been generally used in
diseases of debility, in fevers of the typhoid type, and in gangrene. It
was first conjectured to be useful in gout by Sydenham, and Dr. Haygarth
has strongly recommended its exhibition in acute rheumatism; when
however it is used in these diseases, the greatest attention ought to be
paid to the state of the bowels, and purgatives should be occasionally
interposed. In Dyspepsia, the use of the purer bitters is to be greatly
preferred to that of the bark. OFFICINAL PREPARATIONS. _Infus.
Cinchonæ_, L.E.D. _Decoct. Cinchon._ L.E.D. _Extractum Cinchon._ L.E.
_Extract. Cinchonæ resinosum._ L.D. _Tinct. Cinchonæ_, L.E.D. _Tinct.
Cinchonæ comp._ L.E.D. _Tinct. Cinchon. Ammoniat._ L. MAGISTRAL FORMULÆ,
31, 37, 40, 44, 127. ADULTERATIONS. The frauds committed under this head
are most extensive; it is not only mixed with inferior barks, but
frequently with genuine bark, the active constituents of which have been
entirely extracted by decoction with water. In selecting cinchona bark,
the following precautions may be useful; it should be dense, heavy and
dry, not musty, nor spoiled by moisture; a decoction made of it should
have a reddish colour when warm; but when cold, it should become paler,
and deposit a brownish red sediment. When the bark is of a dark _colour_
between red and yellow, it is either of a bad species, or it has not
been well preserved. Its _taste_ should be bitter, with a slight
acidity, but not nauseous, nor very astringent; when chewed, it should
not appear in threads, nor of much length; the _odour_ is not very
strong, but when bark has been well cured, it is always perceptible, and
the stronger it is, provided it be pleasant, the better may the bark be
considered. In order to give bark the form of _quill_, the bark
gatherers not unfrequently call in the aid of artificial heat, by which
its virtues are deteriorated; the fraud is detected by the colour being
much darker, and upon splitting the bark, by the inside exhibiting
stripes of a whitish sickly hue. In the form of powder, cinchona is
always found more or less adulterated. During a late official inspection
of the shops of apothecaries and druggists, the Censors repeatedly met
with powdered cinchona having a harsh metallic taste, quite foreign to
that which characterizes good bark.[471] The best test of the goodness
of bark is afforded by the quantity of _Cinchonia_, or _Quina_ that may
be extracted from it; and the manufacturer should always institute such
a trial before he purchases any quantity, taking a certain number of
pieces indiscriminately from the bulk. Much has been said of late
concerning the probability of the genuine species of the cinchona tree
becoming extinct; in consequence of which some succedaneum has been
anxiously sought for; the bark of the broad-leaved willow, _Salix
Caprea_, has been proposed for this purpose. Vogel recommends the root
of _Geum urbanum avens_; others propose that of the _Dastisca canabina_.
The _Cinchona Caribæa_ of the Edinburgh Pharmacopœia is said, by Dr.
Wright, to whom we are indebted for our knowledge of it, to have
satisfactorily answered in all cases where the Peruvian bark was
indicated. The _Geoffræa Intermis_ is often sold for it.
M. Ré, Professor of the Materia Medica at the Veterinary School at
Turin, has announced that the _Lycopus Europæus_ of Linnæus, called by
the peasants of Piedmont the _Herb China_, is a complete succedaneum for
Peruvian Bark.[472] The success with which bark has been imitated by
medicinal combination, has already been noticed in the first part of
this work.