_Hemlock Leaves_; F. _Feuilles de Ciguë_; G. _Schierlingsblätter_.
=Botanical Origin=—_Conium maculatum_ L., see p. 299.
=History=—See p. 299.
=Description=—Hemlock in its first year produces only a tuft of leaves;
but in its second a stout erect stem which often grows to the height
of 5 or 9 feet, is much branched in its upper part, and terminates in
small umbels, each having about 12 rays. The lower leaves, often a foot
in length, have a triangular outline, and a hollow stalk as long as the
lamina, clasping the stem at its base with a membranous sheath. Towards
the upper portion of the plant, the leaves have shorter stalks, are
less divided, and are opposite or in cohorts of 3 to 5. The involucral
bracts are lanceolate, reflexed, and about a ¼ of an inch long. Those
of the partial umbel are turned towards the outside, and are always 3
in number. The larger leaves are twice or thrice pinnate, the ultimate
segments being ovate-oblong, acute, and deeply incised.
The stem is cylindrical and hollow, of a glaucous green, generally
marked on its lower part with reddish-brown spots. The leaves are of a
dull dark green, and like the rest of the plant quite glabrous. They
have when bruised a disagreeable fœtid smell.
For medicinal purposes the plant should be taken when in full
blossom.[1152]
=Chemical Composition=—The leaves of hemlock contain, though in
exceedingly small proportion, the same alkaloids as the fruits. Geiger
obtained from the fresh herb not so much as one ten-thousandth part
of conine. It is probable however that the active constituents vary
in proportion considerably, and that a dry and sunny climate promotes
their development.
The same observer, as well as Pereira, has pointed out that hemlock
leaves when dried are very frequently almost devoid of conine, and
the observation is supported by the more recent experiments of Harley
(1867). It has also been shown by the last named physician, that the
inspissated juice known in pharmacy as _Extractum Conii_ usually
contains but a mere trace of alkaloid, the latter having in fact been
dissipated by the heat employed in reducing the juice to the required
consistence. On the other hand, Harley has proved that the juice of
fresh hemlock preserved by the addition of spirit of wine, as in the
_Succus Conii_ of the Pharmacopœia, possesses in an eminent degree the
poisonous properties of the plant.
[1150] _Trans. of the New York State Medical Society_ for 1867.
[1151] _The old Vegetable Neurotics_, Lond. 1869.
[1152] The London herbalists often collect it while much of the
inflorescence is still in bud, in which state it affords far more of
leaf than when well matured; but it is in the latter condition that the
plant is to be preferred.
The entire amount of nitrogen in dried hemlock leaves was estimated by
Wrightson (1845) at 6·8 per cent.; the ash at 12·8 per cent. The latter
consists mainly of salts of potassium, sodium, and calcium, especially
of sodium chloride and calcium phosphate.
A ferment-oil may be obtained from _Conium_; it is stated to have an
odour unlike that of the plant and a burning taste, and not to be
poisonous.[1153]
[1153] Gmelin, _Chemistry_, xiv. 405.
=Uses=—Hemlock administered in the form of _Succus Conii_, has a
peculiar sedative action on the motor nerves, on account of which it
is occasionally prescribed. It was formerly much more employed than at
present, although the preparations used were so defective that they
could rarely have produced the specific action of the medicine.
=Plants liable to be confounded with Hemlock=—Several common plants of
the order _Umbelliferæ_ have a superficial resemblance to _Conium_, but
can be discriminated by characters easy of observation. One of these is
_Æthusa Cynapium_ L. or _Fool’s Parsley_, a common annual garden weed,
of much smaller stature than hemlock. It may be known by its primary
umbel having no involucre, and by its partial umbel having an involucel
of 2 or 3 linear pendulous bracts. The ridges of its fruit moreover are
not wavy or crenate as in hemlock, nor is its stem spotted.
_Chærophyllum Anthriscus_ L. (_Anthriscus vulgaris_ Pers.) and two
or three other species of _Chærophyllum_ have the lower leaves not
unlike those of hemlock, but they are _pubescent_ or _ciliated_. The
fruits too are _linear-oblong_, and thus very dissimilar from those of
_Conium_.
The latter plant is in fact clearly distinguished by its smooth spotted
stem, the character of its involucral bracts and fruit, and finally by
the circumstance that when triturated with a few drops of solution of
caustic alkali, it evolves conine (and ammonia), easily observable as
a white fume when a rod moistened with strong acetic acid is held over
the mortar.