=History=—Dr. Coxe of Philadelphia was the first to suggest that
the juice of the lettuce, collected in the same manner as opium is
collected from the poppy, might be usefully employed in medicine. The
result of his experiments on the juice which he thus obtained from
the garden lettuce (_L. sativa_ L.), and called _Lettuce Opium_, was
published in 1799.[1455]
The experiments of Coxe were continued some years later by Duncan,
Young, Anderson, Scudamore and others in Scotland, and by Bidault
de Villiers and numerous observers in France. The production of
lactucarium in Auvergne was commenced[1456] by Aubergier, pharmacien of
Clermont-Ferrand, about 1841.
=Secretion=—All the green parts of the plant are traversed by a
system of vessels, which when wounded, especially during the period
of flowering, instantly exude a white milky juice. The stem, at first
solid and fleshy but subsequently hollow, owes its rigidity to a circle
of about 30 fibro-vascular bundles, each of which includes a cylinder
of cambium. At the boundary between this tissue and the primary
cortical parenchyme, is situated the system of milk-vessels, exhibiting
on transverse section a single or double circle of thin-walled tubes,
the cavities of which contain dark brown masses of coagulated juice.
In longitudinal section, they appear branched and transversely bound
together, as in the milk-vessels of taraxacum. The larger of these
tubes, 35 mkm. in diameter, correspond pretty regularly in position
with the vascular bundles. Each of the latter is also separated from
the pith by a band or arch of cambium, in the circumference of which
isolated smaller milk-vessels occur.
The system of milk-vessels[1457] is therefore double, belonging to
the pith on the one side, and to the bark on the other, the two being
separated by juiceless wood. The milk-vessels of the bark are covered
by only 2 to 6 rows of parenchyme-cells of the middle bark, rapidly
decreasing in size from within outwards, and these are protected by a
not very thick-walled epidermis. Hence it is easy to understand how the
slightest puncture or incision may reach the very richest milk-cells.
[1453] The term Thridace is also applied to _Extract of Lettuce_.
[1454] The authors of the French _Codex_ of 1866 name as the source of
lactucarium that form of the garden lettuce which has been called by
DeCandolle _Lactuca capitata_. Maisch has obtained lactucarium from _L.
elongata_ Mühl. (_Am. Journ. of Pharm._ 1869. 148).
[1455] Inquiry into the comparative effects of the _Opium officinarum_,
extracted from the _Papaver somniferum_ or _White Poppy_ of Linnæus,
and that procured from the _Lactuca sativa_ or _Common cultivated
Lettuce_ of the same author.—_Transact. of the American Philosophical
Society_, iv. (1799) 387.
[1456] _Comptes Rendus_, xv. (1842) 923.
[1457] Beautifully delineated by Hanstein in the work referred to at p.
352, note 2; see also Trécul, _Ann. des Sciences nat. Bot._ v. (1866)
69; Dippel, _Entstehung der Milchsaftgefässe_, Rotterdam, 1865. tab. 1.
fig. 17.
The drops of milky juice, when exposed to the air, quickly harden to
small yellowish-brown masses, whitish within.
=Collection and Description=—Lactucarium has been especially collected
since about the year 1845, in the neighbourhood of the small town of
Zell on the Mosel between Coblenz and Trèves in Rhenish Prussia. The
introduction of this industry is due to Mr. Goeris, apothecary of that
place, to whom we are indebted for the following information, and for
some further particulars, to Mr. Meurer of Zell.
The plant is grown in gardens, where it produces a stem only in its
second year. In May just before it flowers, its stem is cut off at
about a foot below the top, after which a transverse slice is taken
off daily until September. The juice, which is pure white but readily
becomes brown on the surface, is collected from the wounded top by
the finger, and transferred to hemispherical earthen cups, in which
it quickly hardens so that it can be turned out. It is then dried in
the sunshine until it can be cut into four pieces, when the drying is
completed by exposure to the air for some weeks on frames.
At Zell, 300 to 400 kilogrammes (661 to 882 lb.) of lactucarium
are annually produced; the whole district furnishes at best but 20
quintals annually. The price the drug fetches on the spot varies from
4 to 10 thalers per kilogramme (about 6_s._ to 14_s._ per lb.) In the
Eifel district, where lactucarium was formerly collected, none is now
produced.
As found in trade, German lactucarium consists of angular pieces formed
as already described, but rendered more or less shrunken and irregular
by loss of moisture and by fracture. Externally they are of a dull
reddish-brown, internally opaque and wax-like, and when recent, of a
creamy white. By exposure to the air, this white becomes yellow and
then brown. Lactucarium has a strong unpleasant odour, suggestive of
opium, and a very bitter taste.
The lactucarium produced by Aubergier of Clermont-Ferrand is of
excellent quality, but does not appear to differ from that obtained
on the Mosel, except that it is in circular cakes about 1½ inches in
diameter, instead of in angular lumps.
Scotch lactucarium, which was formerly the only sort found in the
market, is still (1872) met with. Mr. Fairgrieve, who produces it in
the neighbourhood of Edinburgh, collects the juice into little tin
vessels, in which it quickly thickens; it is then turned out and dried
with a gentle heat, the drug being broken up as the process of drying
goes on. It is thus obtained in irregular earthy-looking lumps of a
deep brown hue, of which the larger may be about an inch in length. In
smell, it exactly resembles the drug collected on the Continent.[1458]
[1458] We are indebted to Mr. H. C. Baildon for a specimen of Scotch
lactucarium collected about the year 1844, and to Messrs. T. and H.
Smith for a sample of Mr. Fairgrieve’s article.
We have also before us Austrian lactucarium, prepared at Waidhofen on
the Thaya, where about 35 kilogrammes are annually produced. It is in
fine tears of vigorous smell.
We are unacquainted with Russian lactucarium, which has been quoted at
a very high price in some continental lists.
=Chemical Composition=—Lactucarium is a mixture of very different
organic substances, together with 8 to 10 per cent. of inorganic
matter. It is not completely taken up by any solvent, and when heated
merely softens but does not melt. Nearly half the weight of lactucarium
consists of a substance called _Lactucerin_ or _Lactucon_, which in our
opinion is closely allied to if not identical with similar substances
occurring in numerous milky juices. Lactucerin as afforded by the drug
under examination is probably a mixture of several bodies. It may be
obtained by exhausting lactucarium with boiling alcohol sp. gr. 0·830;
it is deposited in crystals, which when duly purified have the form of
slender colourless, microscopic needles. Lactucerin is an inodorous,
tasteless substance, insoluble in water, but dissolving in ether and in
oils both fixed and volatile, not quite so readily either in benzol, or
in bisulphide of carbon. We found it to melt at 232° C. and to agree
with the formula C₁₉H₃₀O; Franchimont (1879) assigns to it the formula
C₁₄H₂₄O, melting point 296°.
Euphorbon (see Euphorbium), echicerin (see Cortex Alstoniæ),
taraxacerin (p. 394), the cynanchol, C₁₅H₂₄O, extracted in 1875 by
Buttleroff from _Cynanchum acutum_ L., are remarkably analogous to
lactucerin.
In the lactucarium of Zell, we further met with a large amount of a
substance which is readily soluble in bisulphide of carbon. It is an
amorphous mass, melting below 100°, separating from alcohol as a syrupy
mass.
Cold alcohol, as well as boiling water, takes out of lactucarium
about 0·3 per cent. of a crystallizable bitter substance, _Lactucin_,
C₁₁H₁₂O₃H₂O, which although it reduces alkaline cupric tartrate, is
not a glucoside. It may be best obtained by means of dialyse. Lactucin
forms white pearly scales, readily soluble in acetic acid, but
insoluble in ether. It loses its bitterness when treated with an alkali.
From the mother-liquors that have yielded lactucin, Ludwig, in
1847, obtained _Lactucic Acid_, as an amorphous light yellow mass,
becoming crystalline after long standing. Lastly lactucarium has
further afforded in small quantity an amorphous substance named
_Lactucopicrin_, C₄₄H₆₄O₂₁, apparently produced from lactucin by
oxidation; it is stated by Kromayer (1862) to be soluble in water or
alcohol, and to be very bitter.
Of the widely diffused constituents of plants, lactucarium contains
caoutchouc (40-50 per cent.), gum, oxalic, citric, malic and succinic
acids, sugar, mannite, and asparagin, together with potassium, calcium
and magnesium salts of nitric and phosphoric acids. We obtained
crystals of nitrate of potassium by concentrating the aqueous decoction
of lactucarium. On distillation with water, a volatile oil having the
odour of lactucarium passes over in very small quantity.
=Uses=—The soporific powers universally ascribed in ancient times
to the lettuce are supposed to exist in a concentrated form in
lactucarium. Yet numerous experiments have failed to show that this
substance possesses more than very slight sedative properties, if
indeed it is not absolutely inert.[1459]