_Lupulina_; _Lupulin_, _Lupulinic Grains_; F. _Lupuline_; G.
_Hopfendrüsen_, _Hopfenstaub_.
=Botanical Origin=—_Humulus Lupulus_ L. (see preceding article). The
minute, shining, translucent glands of the strobile constitute when
detached therefrom the substance called _Lupulin_.
=History=—The glands of hop were separated and chemically examined by
L. A. Planche, a pharmacien of Paris, whose observations were first
briefly described by Loiseleur-Deslongchamps in 1819.[2060] In the
following year, Dr. A. W. Ives of New York[2061] published an account
of his experiments upon hops and their glands, to which latter he
applied the name of _Lupulin_. Payen and Chevallier, Planche and
others, made further experiments on the same subject, endorsing the
recommendation of Ives that lupulin (or, as they preferred to call it,
_Lupuline_) might be advantageously used in medicine in place of hops.
[2059] _Annual Statement of the Trade of the United Kingdom_ for 1872.
49. 93.
[2060] _Manuel des Plantes usuelles et indigènes_, 1819. ii. 503.
[2061] Silliman’s _Journ. of Science_, ii. (1820) 302.
=Production=—Lupulin is obtained by stripping off the bracts of hops,
and shaking and rubbing them; and then separating the powder by a
sieve. The powder thus detached ought to be washed by decantation,
so as to remove from it the sand or earth with which it is always
contaminated; finally it should be dried, and stored in well-closed
bottles. From the dried strobiles, 8 to 12 per cent. of lupulin may be
obtained.
=Description=—Lupulin seen in quantity appears as a yellowish-brown
granular powder, having an agreeable odour of hops and a bitter
aromatic taste. It is gradually wetted by water, instantly by alcohol
or ether, but not by potash or sulphuric acid. By trituration in a
mortar the cells are ruptured so that it may be worked into a plastic
mass. Thrown into the air and then ignited, it burns with a brilliant
flame like lycopodium.
=Microscopic Structure=—The lupulinic gland or grain, like the
generality of analogous organs, is formed by an intumescence of the
cuticle of the nuculæ and bracts of hop (see p. 552). Each grain
is originally attached by a very short stalk, which is no longer
perceptible in the drug. The gland, exhausted by ether and macerated in
water, is a globular or ovoid thin-walled sac, measuring from 140 to
240 mkm. It consists of two distinct, nearly hemispherical parts; that
originally provided with the stalk is built up of tabular polyhedric
cells, whilst the upper hemisphere shows a continuous delicate
membrane. This part therefore easily collapses, and thus exhibits a
variety of form, the greater also as the grains turn pole or equator to
the observer.[2062]
The hop gland is filled with a thick, dark brown or yellowish liquid,
which in the drug is contracted into one mass occupying the centre of
the gland. It may be expelled in minute drops when the wall is made to
burst by warming the grain in glycerin. The colouring matter, to which
the wall owes its fine yellow colour, adheres more obstinately to the
thinner hemisphere, and is more easily extracted from the thicker part
by means of ether.
=Chemical Composition=—The odour of lupulinic grains resides in the
essential oil, described in the previous article. The bitter principle
formerly called _Lupulin_ or _Lupulite_ was first isolated by Lermer
(1863) who called it the _bitter acid of hops_ (_Hopfenbittersäure_).
It crystallizes in large brittle rhombic prisms, and possesses in a
high degree the peculiar bitter taste of beer, in which however it can
be present only in very small proportion, it being nearly insoluble in
water, though easily dissolved by many other liquids. The composition
of this acid, C₃₂H₅₀O₇, appears to approximate it to absinthiin; it is
contained in the glands in but small proportion. Still smaller is the
amount of another crystallizable constituent, regarded by Lermer as an
alkaloid.
The main contents of the hop gland consist of wax (_Myricylic
palmitate_, according to Lermer), and resins, one of which is
crystalline and unites with bases.
A good specimen of German lupulin, dried over sulphuric acid, yielded
us 7·3 per cent. of ash. The same drug exhausted by boiling ether,
afforded 76·8 per cent. of an extremely aromatic extract, which on
exposure to the steam-bath for a week, lost 3·03 per cent., this loss
corresponding to the volatile oil and acids. The residual part was
soluble in glacial acetic acid and could therefore contain but very
little fatty matter.
=Uses=—The drug has the properties of hops, but with less of
astringency. It is not often prescribed.
=Adulteration=—Lupulin is apt to contain sand, and on incineration
often leaves a large amount of ash. Other extraneous matters which
are not unfrequent may be easily recognized by means of a lens. As
the essential oil in lupulin is soon resinified, the latter should be
preferred fresh, and should be kept excluded from the air.
[2062] For a full account of the formation of the glands, see Trécul,
_Annales des Sciences Nat._, Bot., i. (1854) 299. An abstract may be
found in Méhu’s _Etude du Houblon et du Lupulin_, Montpellier, 1867.