This is a subject of far greater importance than is usually assigned to
it, as will be more fully explained in the sequel.
1. Many substances, as _vegetable extracts_, may be formed into pills
without any addition; others, as _gum resins_, become sufficiently soft
by being beaten, or by the addition of a drop or two of spirit, or
_liquor potassæ_. Some dry substances react upon each other, and
produce, without the addition of any foreign matter, soft and
appropriate masses. The _Pilulæ Ferri Compositæ_, of our Pharmacopœia
afford a very striking example of this peculiar change of consistence,
which the mutual reaction of the ingredients produces by simple triture.
The _Pilulæ Aloes Compositæ_ offer another instance; for the extract of
gentian, upon being triturated with aloes, produces a very soft mass, so
that the addition of a syrup, as directed by the Pharmacopœia, is quite
unnecessary. See _Form: 12_.
2. Many substances are, in themselves, so untractable, that the addition
of some matter foreign to the active ingredients, is absolutely
essential for imparting convenience of form. It is generally considered
that very little skill and judgment is required in the selection of such
a substance, provided it can fulfil the _mechanical_ intention just
alluded to—the fact however is, that _the medicinal power of the pill
may be materially controlled, modified, or even subverted, by the mode
in which it is formed into a mass_. Where the active element of a pill
is likely to be improved by minute division, a gummy or resinous
constituent may be usefully selected: under the history of Aloes, I have
alluded to a popular pill, known by the name of the _dinner-pill_, in
which case the _mastiche_ divides the particles of the aloes, and
modifies the solubility of the mass. The _Pilulæ Opii_ of the former
Pharmacopœia of London, consisted of equal proportions of opium and
extract of liquorice, and the mass was so insoluble that its effects
were extremely uncertain and precarious; in the present edition, soap
has been very judiciously substituted; but in certain cases where we
wish to protract the influence of opium, or that of any other active
body, so as not to obtain its full effects at once, we may very
advantageously modify its solubility by combining it with a gum resin or
some substance which will have the effect of retarding its solution in
the stomach. The _Pilulæ Styrace_ of the Dublin college, presents itself
as an efficient example of this species of pharmaceutical address; see
also _Form. 10, 11, 12_. I am well acquainted with many formulæ whose
utility has been sanctioned by experience, and I have no hesitation in
believing that their salutary mode of operation would receive a
plausible explanation from this simple law of combination. Dr. Young has
very justly stated in his Medical Literature,[297] that the _balsam of
copaiba_ envelopes metallic salts, so as to lessen their activity; he
says that the sub-carbonate of iron, made into pills with copaiba, was
given for some weeks without any apparent effect; and that a few hours
after the same quantity had been given, with gum only, the fæces were
perfectly black. I do not know a more striking and instructive proof of
the influence of a glutinous or viscid constituent, in wrapping up a
metallic salt, and defending the stomach from its action, than is
presented in the case published by the medical attendant Mr. Marshall,
in consequence of the attempt of Eliz. Fenning to poison the family of
Mr. Turner of Chancery-lane by arsenic, which she providentially
administered in a heavy yeast dumpling. _Soap_ is very frequently used
for the formation of pill-masses, and it is an excellent constituent for
substances likely to be injured by meeting with an acid in the _primæ
viæ_; many resinous bodies may also be reduced to a proper consistence
by soap, although in prescribing it, its levity should be attended to,
or otherwise the pills will be too bulky; in general it will combine
with an equal portion of any resinous powder, as _Rhubarb_, _Jalap_,
_&c._; it is of course ineligible where the substances are decomposed by
alkalies, as _Tartarized Antimony_; this last precaution will also apply
to _aromatic confection_ as a vehicle, on account of the carbonate of
lime contained in it. The _Conserve of Roses_ has the advantage of
retaining its consistency much longer than mucilage, but as it contains
an uncombined acid, it is frequently inadmissible; it could not for
instance be with propriety employed with the precipitated sulphuret of
antimony. Pills made with mucilage, are apt to crumble when they are
rolled out; this is the case with the _Pilulæ Hydrargyri submuriatis_;
some extract therefore would be a more convenient constituent; in this
particular case, however, the addition of a few drops of spirit would
supersede the necessity of _any_ constituent. Castor oil, in some cases,
especially with some of the harder purgative extracts, will impart an
eligible consistence.
_Crumb of bread_, furnishes a convenient vehicle for those salts which
are ponderous, active in very small doses, or which are liable to be
decomposed by other vehicles; but an objection is attached even to this,
for it is liable to become so dry and hard when kept, that pills made
with it will frequently pass undissolved. Swediaur mentions this fact
with reference to Plenck’s mercurial pill, as well as to one of
corrosive sublimate, and he proposes for this reason to substitute
_starch_; the addition however of a small portion of sugar will prevent
the bread from becoming thus indurated, and with such a precaution it
may be very safely employed. For the purpose of forming active vegetable
powders into pills, such as _Digitalis, Conium_, &c., I am informed by
Mr. Hume of Long Acre, that in his experience _melasses_ or _treacle_ is
the best constituent that can be selected, for it undergoes no
decomposition by time, but maintains a proper consistency, and preserves
the sensible qualities of the plant quite unimpaired for many years. I
have deposited in the cabinet of the College, specimens of such pills,
of _hemlock_ and _foxglove_, which retain the characteristic odour of
these vegetables, notwithstanding they have been now made for several
years. _Honey_ has likewise the property of preserving vegetable
substances; _seeds_ may be kept in it for any length of time, some of
which, on being taken out, washed, and planted, will even vegetate. It
has also been used for the preservation of animal matter; the bodies of
the Spartan kings, who fell at a distance in battle, were thus
preserved, in order that they might be carried home.[298]
_Water_ will on some occasions be found a convenient expedient; powdered
_Rhubarb_ or _Jalap_ may be thus made into masses without any increase
of bulk, but the pills will be apt, if kept, to become mouldy.
3. In the formation of pills the ingredients should be hastily rubbed
together, whenever they are liable to be injured by long exposure to the
air; thus in the formation of _Pilulæ Hydrargyri submuriatis compositæ_,
the compound is rendered less active by too long continued triture. See
_Pulveres_.
4. In dividing pill-masses, it is usual to add to them, and envelope
them in, magnesia; where calomel is present, I have satisfied myself by
experiment that a _muriate of magnesia_ is formed under such
circumstances, and it is owing to this partial decomposition, that the
surface of the pill exhibits a greenish hue; starch, powder of
liquorice,[299] or orrice root, might perhaps under such circumstances
be more judiciously preferred. In Germany, the powder of _Lycopodium_ is
generally used. Formerly, the pill was covered with gold leaf, which
protected it from the influence of the stomach, and frequently rendered
it unavailing.
It has been observed that many of the pill-masses directed in our
Pharmacopœias, are liable to become so hard[300] and dry by being kept,
that they are unfit for that division for which they were originally
intended; indeed Dr. Powel considers it doubtful whether the greater
number of articles had not better be kept in powder, and their
application to the formation of pills left to extemporaneous direction;
the necessity of this is farther apparent, when we learn that it is a
common practice for the dispenser to soften these masses by the
application of a hot spatula, or pestle, which sometimes carbonizes, and
frequently decomposes them.