_Manna_; F. _Manne_; G. _Manna_.
=Botanical Origin=—_Fraxinus Ornus_ L. (_Ornus europæa_ Pers.), the
Manna-ash, is a small tree found in Italy, whence it extends northwards
as far as the Canton of Tessin in Switzerland and the Southern Tyrol.
It also occurs in Hungary (Buda) and the eastern coasts of the
Adriatic, in Greece, Turkey (Constantinople), in Asia Minor about
Smyrna and at Adalia on the south coast. It grows in the islands of
Sicily, Sardinia and Corsica, and is found in Spain at Moxente in
Valencia.[1502] As an ornamental tree it has been introduced into
Central Europe, where it is often seen of greater dimensions, sometimes
acquiring a height of about 30 feet. It blossoms in early summer,
producing numerous feathery panicles of dull white flowers which give
it a pleasing appearance. The foliage exhibits great variation in shape
of leaflets, even where the tree is uncultivated; and the fruits also
are very diverse in form.
In some districts of Sicily, a little manna is obtained from the Common
Ash, _F. excelsior_ L.
[1499] _Blue Book_ for the Colony of the Straits Settlements,
Singapore, 1872.
[1500] _Consular Reports_, August 1873. 953.
[1501] _Statement of the Trade and Navigation of the Presidency of
Bombay for 1871-72_, pt. ii. 26. 79.
[1502] _Fraxinus Bungeana_ DC., a tree of Northern China, appears to be
hardly distinct from _F. Ornus_.
=History=—The name _Manna_, though originally applied to the aliment
miraculously provided for the sustenance of the ancient Israelites
during their journey to the Holy Land, has been used to designate other
substances of distinct nature and origin. Of these, the best known and
most important is the saccharine exudation of _Fraxinus Ornus_ L.,
which constitutes the _Manna_ of European medicine.
It appears evident[1503] that previous to the 15th century, the manna
in Europe was imported from the East and was not that of the ash.
Raffaele Maffei, called also Volaterranus, a writer who flourished
in the second half of the 15th century, states that manna began to
be gathered in Calabria in his time, but that it was inferior to the
oriental.[1504] At this period the manna collected was that which
exuded spontaneously from the leaves of the tree, and was termed _Manna
di foglia_ or _Manna di fronda_: that which flowed from the stem bore
the name of _Manna di corpo_ and was less esteemed. All such manna was
very dear.
About the middle of the 16th century, the plan of making incisions in
the trunk and branches was resorted to, and although it was strenuously
opposed even by legislative enactment, the more copious supplies which
it enabled the collectors to obtain led it to being generally adopted.
The Ricettario Fiorentino of the year 1573[1505] states that the manna
“fatta con arte,” _i.e._ obtained by incisions, came from Cosenza in
Calabria and differed not little from Syrian “manna mastichina.”[1506]
_Manna di foglia_ became in fact utterly unknown, so that Cirillo
of Naples, writing in 1770, expresses doubt whether it ever had any
existence.[1507]
With regard to the history of manna-production in Sicily, there is
this curious fact, that near Cefalù there exists an eminence in the
Madonia range, called _Gebelman_ or _Gibelmanna_, which in Arabic
signifies _manna-mountain_. This name is not of modern origin, but is
found in a diploma of the year 1082, concerning the foundation of the
bishopric of Messina; and it has been held to indicate that manna was
there collected during the Saracenic occupation of Sicily, A.D. 827 to
1070. We have not been successful in finding any evidence whether this
supposition is well founded. On the other hand, it is remarkable that
no writer, so far as we know, mentions manna as a production of Sicily,
before Paolo Boccone of Palermo, who, after naming many localities
for the drug in continental Italy, states that it is also obtained in
Sicily.[1508]
Manna was also produced until recently in the Tuscan Maremma, but
neither from that locality, nor from the States of the Church, where it
was collected in the time of Boccone, is any supply now brought into
commerce, though the name of Tolfa, a town near Civita Vecchia, is
still used to designate an inferior sort of the drug.
The collection of manna in Calabria, which was imported up to the end
of last century, has now almost entirely ceased.[1509]
[1503] Hanbury, _Historical Notes on Manna_, _Pharm. Journ._ xi. (1870)
326; or _Science Papers_, 355.
[1504] _Commentarii Urbani_, Paris, 1515. lib. 38. f. 413.
[1505] P. 46; we have not seen the edition of 1498.
[1506] Mastichina alludes probably to the granular form of that
manna—perhaps it was that of Alhagi, which we shall mention further on,
p. 414.
[1507] _Phil. Trans._ lx. (1771) 233.
[1508] _Museo di Fisica_, Venet. 1697. Obs. xiv.-xv.
[1509] Hanbury in _Giornale Botanico Italiano_, Ottobre 1872. 267;
_Pharm. Journ._ Nov. 30. 1872. 421; _Science Papers_, 365.
=Production=—The manna of commerce is collected at the present day
exclusively in Sicily. The principal localities producing the drug
are the districts around Capaci, Carini, Cinisi, and Favarota, small
towns 20 to 25 miles west of Palermo near the shores of the bay of
Castellamare; also the townships of Geraci, Castelbuono, and other
places in the district of Cefalù, 50 to 70 miles eastward of Palermo.
The manna-ash, in the districts whence the best manna is obtained, does
not at the present day form natural woods, but is cultivated in regular
plantations called _frassinetti_. The trees, which attain a height of
from 10 to 20 feet, are planted in rows and stand about 7 feet apart,
the soil between being at times loosened, kept free from weeds, and
enriched by manure. After a tree is 8 years old and when its stem is at
least 3 inches in thickness, the gathering of manna may begin; and may
continue for 10 or 12 years, when the stem is usually cut down, and a
young one brought up from the same root takes its place. The same stump
thus has often two or three stems rising from it.
To obtain manna, transverse cuts from 1½ to 2 inches long and 1 inch
apart, are made in the bark, just reaching to the wood. One cut is made
daily, beginning at the bottom of the tree, the second directly above
the first, and so on while dry weather lasts. In the following year,
cuts are made in the untouched part of the stem, and in the same way
in succeeding seasons. When after some years the tree has been cut all
round and is exhausted, it is felled. Pieces of sticks or straws are
inserted in the incisions, and become encrusted with the very superior
manna, called _Manna a cannolo_, which however is unknown in commerce
as a special sort. The fine manna ordinarily seen appears to have
hardened on the stem of the tree. The manna which flows from the lower
incisions, and is often collected on tiles or on a cup-shaped piece of
the stem of the prickly pear (_Opuntia_), is less crystalline, and more
gummy and glutinous, and is regarded of inferior quality.
The best time for notching the stems is in July and August, when the
trees have ceased to push forth more leaves. Dry and warm weather is
essential for a good harvest. The manna after removal from the tree,
is laid upon shelves in order that it may dry and harden before it is
packed. The masses left adhering to the stem after the finer pieces
have been gathered, are scraped off and form part of the _Small Manna_
of commerce.[1510]
=Secretion=—We have examined microscopically the bark of stems of
_Fraxinus Ornus_ that had been incised for manna at Capaci. It exhibits
no peculiarity explaining the formation of manna, or any evidence that
the saccharine exudation is due to an alteration of the cell-walls
as in the case of tragacanth. The bark is poor in tannic matter; it
contains starch, and imparts to water a splendid fluorescence due to
the presence of _Fraxin_.
[1510] Our account of the production of manna has been derived from
the observations of Stettner, who visited Sicily in the summer of 1847
(_Archiv der Pharm._ iii. 194; also Wiggers’ _Jahresbericht_, 1848.
35; _Hooker’s Journ. of Bot._ i. 1849. 124), from those of Cleghorn
(_Trans. of the Bot. Soc. of Edinburgh_, x. 1868-69. 132), and from
personal investigations made by one of us in the neighbourhood of
Palermo in May 1872. See Hanbury, _Science Papers_, 367.
=Description=—Various terms have been used by pharmacological writers
to designate the different qualities of manna, but in English commerce
they are not now employed; and the better kinds of the drug are called
simply _Flake Manna_, while the smaller pieces, usually loosely
agglutinated and sold separately, are termed _Small Manna_ or _Tolfa
Manna_.
Owing to the gradual exudation of the juice and the deposition of one
layer over another, manna has a stalactitic aspect. The finest pieces
are mostly in the form of three-edged sticks, sometimes as much as 6
to 8 inches long and an inch or more wide, grooved on the inner side,
which is generally soiled by contact with the bark; of a porous,
crystalline, friable structure and of a pale brownish yellow tint,
becoming nearly pure white in those parts which have been most distant
from the bark of the tree. The pieces which are of deeper colour, and
of an unctuous or gummy appearance, are less esteemed. Good manna is
crisp and brittle, and melts in the mouth with an agreeable, honey-like
sweetness, not entirely devoid of traces of bitterness and acridity.
Its odour may be compared to that of honey or moist sugar.
Manna of the best quality dissolves at ordinary temperatures in about
six parts of water, forming a clear, neutral liquid. It contains
besides mannite, a small proportion of sugar and gum.
The manna which exudes from the older stems and from the lower parts
of even young trees, contains more or less considerable quantities
of gum and fermentable sugar, as well as extraneous impurities. The
less favourable weather of the later summer and autumn promotes an
alteration in the composition of the juice, and impairs its property of
concreting into a crystalline mass.
=Chemical Composition=—The predominant constituent of manna, at least
of the better sorts, is _Manna-sugar_ or _Mannite_, C₆H₈(OH)₆ which
likewise occurs, though in much smaller quantity, in many other plants
besides _Fraxinus_. Artificially, it is produced by treating glucose,
C₆H₁₂O₆, with sodium amalgam, and indirectly in the fermentation of
glucose or of cane-sugar. It is isomeric with dulcite or melampyrin;
crystallizes in shining prisms or tables, belonging to the rhombic
system; melts at 166° C., and in very small quantity may by careful
heating be sublimed and decomposed. It dissolves in 6·5 parts of water
at 16° C., less freely in aqueous alcohol, very sparingly in absolute
alcohol, and not in ether. The solution has an extremely weak rotatory
power, and is not altered by boiling with dilute acids or alkalis, or
with alkaline cupric tartrate.
Berthelot has shown that mannite is susceptible of fermentation, though
not so easily as sugars belonging to the group of carbo-hydrates. The
quantity of mannite in the best manna varies from 70 to 80 per cent.
When a solution of manna is mixed with alkaline cupric tartrate,
rapid reduction to cuprous hydrate takes place even in the cold. This
effect is due to the presence of a sugar which, according to Backhaus
(1860), consists of ordinary dextro-glucose. It may amount to as
much as 16 per cent., and is found in the best flake manna, but most
abundantly in the unctuous varieties. Buignet[1511] has pointed out
that the rotatory power of this sugar being inconsiderable, it probably
consists of a mixture of _Cane-sugar_ and _Levulose_. He found however
that an aqueous solution of manna deviates powerfully to the right, a
fact which he considers due to the presence of a large proportion of
_Dextrin_. The best kinds of manna, according to Buignet, contain about
20 per cent. of dextrin; the inferior much more.
[1511] _Journ. de Pharm._ vii. (1867) 401; viii. (1868) 5.
In our experiments we have not succeeded in isolating either dextrin or
cane-sugar. There is present, even in the finest manna, a small amount
of a dextrogyre mucilage, which is precipitated by neutral acetate of
lead, and yields mucic acid when boiled with concentrated nitric acid.
Ether extracts from an aqueous solution of manna a very small quantity
of red-brown resin, having an offensive odour and sub-acrid taste;
together with traces of an acid which reduces silver salts and appears
to be easily resinified. The quantity of water in the inferior kinds
of manna often amounts to 10 or 15 per cent. The finest manna affords
about 3·6 per cent. of ash.
The greenish colour of certain pieces of manna was formerly attributed
to the presence of copper, till Gmelin, on account of the fluorescence
of the solution, ascribed it to _Æsculin_. It is in reality produced by
a body much resembling æsculin, namely _Fraxin_, C₁₆H₁₈O₁₀, occurring
in the bark of the manna-ash and of the common ash, and together
with æsculin, in that of the horse-chestnut. Fraxin crystallizes in
colourless prisms, easily soluble in hot water and in alcohol, and
having a faintly astringent and bitter taste. By dilute acids, it is
resolved into _Fraxetin_, C₁₀H₈O₃, and _Glucose_, C₆H₁₂O₆. The presence
of fraxin in manna, especially in the inferior sorts, is made apparent
by the faint fluorescence of the alcoholic manna solution. The smallest
fragment of the bark of the ash or the manna-ash immersed in water
displays the same fluorescence.
=Commerce=—The exports of manna from Sicily[1512] (chiefly from
Palermo) have been as follows:—
1869 1870 1871
2546 cwt., 1564 cwt., 3038 cwt.,
val. £15,972. val. £10,220. val. £19,528.
About half the quantity is sent to France. Italian commercial
statistics[1513] represent the export of manna in 1870 thus:—_in
canelli_ 58,691 kilo. (1155 cwt.), _in sorte_ 186,664 kilo. (3676
cwt.). The United Kingdom imported in the year 1870, 230 cwt. of manna,
valued at £4447.[1514]
[1512] _Report by Consul Dennis on the Commerce and Navigation of
Sicily in 1869, 1870 and 1871._
[1513] Direzione generale delle Gabelle—_Movimento commerciale del
regno d’Italia nel 1870_, Milano, 1871.
[1514] _Annual Statement of the Trade and Navigation of the U.K. for
1870_, p. 102.
In 1877 the exports of “canelli” from Messina were 4273 kilogrammes,
and of the drug “in sorte” 52,874 kilogr.; total value, 127,145 lire.
=Adulteration=—It can hardly be said that manna is subject to
adulteration, though attempts to introduce a spurious manna made of
glucose have been recorded. But considerable skill and ingenuity have
been expended in converting the inferior sorts of manna into what has
the aspect of fine natural Flake Manna, the manufacturers admitting
however the factitiousness of their product. The artificial Flake Manna
has the closest superficial resemblance to very fine pieces of the
natural drug, but differs in its more uniform colour, and in being
uncontaminated with the slight impurities, from which natural manna is
never wholly free. It differs also in that when broken, no crystals of
mannite are to be seen in the interstices of the pieces, and it wants
the peculiar odour and slightly bitter flavour of natural manna. If one
part of it is boiled with four of alcohol (0·838), a viscid honey-like
residue will be obtained, whereas natural manna leaves undissolved a
hard substance. Histed[1515] found it to afford about 40 per cent. of
mannite, while fine manna similarly treated yielded 70 per cent.
=Uses=—A gentle laxative, much less frequently employed in this country
than formerly, but still largely consumed in South America. Mannite,
which possesses similar properties, is often prescribed in Italy.
Other sorts of Manna.
Various plants besides _Fraxinus_ afford, under certain conditions,
saccharine exudations, some of which constituted the _Oriental Manna_
used in Europe in early times. So far as is known, they differ from
officinal manna in containing no mannite.
_Alhagi Manna_; _Turanjabín_ (Arabic); is afforded by _Alhagi
Camelorum_ Fisch. (Hedysarum Alhagi Pallas, non L.), a small spiny
plant of the order _Leguminosæ_ found in Persia, Afghanistan and
Beluchistan. It had already been noticed by Isztachri.[1516] Excellent
specimens of the manna, kindly obtained for us in the north-west of
India by Dr. E. Burton Brown and Mr. T. W. H. Tolbort, show it as a
substance in little roundish, hard, dry tears, varying from the size
of a mustard seed to that of a hemp seed, of a light brown colour,
agreeable saccharine taste, and senna-like smell. The leaflets, spines
and pods of the plant, mixed with the grains of this manna, are
characteristic and easily recognizable.
Villiers (1877) showed this manna to contain cane-sugar, a dextrogyrate
glucose, and _melezitose_ (see further on: Briançon manna, page 416).
Ludwig[1517] had also found some dextrin and mucilage.
Alhagi Manna is collected near Kandahar and Herat, where it is found
on the plants at the time of flowering. It is imported into India
from Kabul and Kandahar to the extent of about 25 _maunds_ (2000 lb.)
annually; its value is reckoned at 30 rupees per _secr_, = 30_s._ per
lb.[1518]
[1515] _On artificial Flake Manna_, in _Pharm. Journ._ xi. (1870) 629.
[1516] Tchihatcheff, _l’Asie mineure_, ii. (1856) 355.
[1517] _Archiv der Pharmacie_, 193 (1870) 32-52.
[1518] Stewart, _Punjab Plants_, Lahore (1869) p. 57; Davies, _Report
on the trade and resources of the countries on the N. W. boundary of
British India_, Lahore, 1862.
_Gaz-anjabin_ (Arabic); _Tamarisk Manna_ (in part)—In the months
of June and July, the shrubs of tamarisk (_Tamarix gallica_ var.
_mannifera_ Ehrenb.) growing in the valleys of the peninsula of Sinai,
especially in the Wady es Sheikh, exude from their slender branches, in
consequence of the puncture of an insect (_Coccus manniparus_ Ehrenb.)
little honey-like drops, which in the coolness of early morning are
found in a solid state. This substance is _Tamarisk Manna_: it is
collected by the Arabs, and by them sold to the monks of St. Katharine,
who dispose of it to the pilgrims visiting the convent. Tamarisk Manna
is also produced (but is perhaps no longer collected?) in Persia,
where it is called _Gaz-angabín_;[1519] and probably likewise in the
Punjab,[1520] from which regions it may have been brought to Europe in
ancient times.
A specimen of tamarisk manna brought from Sinai, examined in 1861 by
Berthelot, had the appearance of a thick yellowish syrup, contaminated
with vegetable remains. It was found to consist of cane-sugar, inverted
sugar (lævulose and glucose), dextrin and water, the last constituting
one-fifth of the whole.[1521]
Although the name _Gaz-angabín_ signifies _tamarisk-honey_, it is
used according to Haussknecht[1522] at the present time in Persia, to
designate certain round cakes, common in all the bazaars, of which the
chief constituent is a manna collected in the mountain districts of
Chahar-Mahal and Faraidan, and especially about the town of Khonsar,
south-west of Ispahan, from _Astragalus florulentus_ Boiss. et
Haussk. and _A. adscendens_ Boiss. et Haussk. The best sorts of this
manna, which are termed _Gaz Alefi_ or _Gaz Khonsari_, are obtained
in August by shaking it from the branches, the little drops finally
sticking together and forming a dirty, greyish-white, tough mass. The
commoner sort got by scraping the stem, is still more impure. The
specimen of it brought by Haussknecht yielded to Ludwig[1523] dextrin,
uncrystallizable sugar and organic acids.
_Shir-khist_—Ancient writers on materia medica as Garcia d’Orta (1563)
mention a sort of manna known by this name. The substance is still
found in the bazaars of North-western India, being imported in small
quantity from Afghanistan and Turkistan.[1524] Haussknecht in his paper
on Oriental Manna already quoted, states that it is the exudation
of _Cotoneaster nummularia_ Fisch. et Mey. (_Rosaceæ_), also of
_Atraphaxis spinosa_ L. (_Polygonaceæ_), and that it is brought chiefly
from Herat. We have to thank Dr. E. Burton Brown of Lahore, and Mr.
Tolbort for specimens of this manna, which, from fragments it contains,
is without doubt derived from a _Cotoneaster_. It is in irregular
roundish tears, from about ¼ up to ¾ of an inch in greatest length,
of an opaque dull white, slightly clammy, and easily kneaded in the
fingers. It has a manna-like smell, a pure sweet taste and crystalline
fracture. With water, it forms a syrupy solution with an abundant
residue of starch granules.
Shír-khist was found by Ludwig to consist of an exudation analogous
to tragacanth, but containing at the same time two kinds of gum, an
amorphous levogyre sugar, besides starch and cellulose.
_Oak Manna_—The occurrence of a saccharine substance on the oak is
noticed by both Ovid and Virgil, and it is also mentioned by the
Arabian physicians, as Ibn Baytar[1525] and Elluchasem Elimithar.[1526]
The last named, who died A.D. 1052, states that the exudation appears
upon the oaks in the region of Diarbekir. At the present day, it is
the object of some industry among the wandering tribes of Kurdistan,
who, according to Haussknecht, collect it from _Quercus Vallonea_
Kotschy and _Q. persica_ Jaub. et Spach. These trees are visited in the
month of August by immense numbers of a small white _Coccus_, from the
puncture of which a saccharine fluid exudes, and solidifies in little
grains. The people go out before sunrise, and shake the grains of manna
from the branches on to linen cloths, spread out beneath the trees. The
exudation is also collected by dipping the small branches on which it
is formed, into vessels of hot water, and evaporating the saccharine
solution to a syrupy consistence, which in this state is used for
sweetening food, or is mixed with flour to form a sort of cake.
[1519] Angelus, _Pharm. Persica_ (see appendix) p. 359.
[1520] Stewart, _op. cit._ p. 92.
[1521] _Comptes Rendus_, liii. (1861) 583; _Pharm. Journ._ iii. (1862)
274.
[1522] _Archiv d. Pharmacie_, 192 (1870) 246.
[1523] _Loc. cit._
[1524] Davies in the work quoted at page 414, note 4.
[1525] Ed. Sontheimer, i. (1840) 375.
[1526] _Tacuini Sanitatis_, Argentorati (1531) 24.
A fine specimen of the Oak Manna of Diarbekir was sent to the London
International Exhibition of 1862. It constituted a moist soft mass of
agglutinated tears, much resembling an inferior sort of ash-manna, and
had an agreeable saccharine taste.
A less pure form of this manna occurs as a compact, greyish, saccharine
mass, sometimes hard enough to be broken with a hammer. It consists
of sugary matter, mixed with abundance of small fragments of green
leaves, and has a herby smell and pleasant sweet taste. A sample of it
brought from Diarbekir, examined by one of us, yielded 90 per cent.
of dextrogyre sugar, which could not be obtained in a crystalline
state, though it exists in such condition in the crude drug. Starch and
dextrine were entirely wanting.[1527]
A specimen furnished to Ludwig[1528] by Haussknecht afforded much
mucilage, a small amount of starch, about 48 per cent. of dextrogyre
grape sugar, with traces of tannic acid and chlorophyll.
_Briançon Manna_—This is a white saccharine substance which, in the
height of summer and in the early part of the day, is found adhering in
some abundance to the leaves of the larch (_Pinus Larix_ L.), growing
on the mountains about Briançon in Dauphiny. It was formerly collected
for use in medicine, but only to a very limited extent, for it was
rare in Paris in the time of Geoffroy (1709-1731), and at the present
day has quite disappeared from trade, though still gathered by the
peasants. A specimen collected for one of us near Briançon in 1854,
consists of small, detached, opaque, white tears, many of them oblong
and channelled, and encrusting the needle-like leaf of the larch; they
have a sweet taste and slight odour.[1529] Under the microscope they
exhibit indistinct crystals.
Briançon manna has been examined in 1858 by Berthelot, who detected
in it a peculiar sugar termed _Melezitose_, answering to the formula
C₁₂H₂₂O₁₁ + OH₂.
Several other saccharine exudations have been observed by travellers
and naturalists; we shall simply enumerate the more remarkable,
referring the reader for further information to the original notices.
_Pirus glabra_ Boiss. affords in Luristan a substance which, according
to Haussknecht, is collected by the inhabitants, and is extremely like
Oak Manna. It is stated by the same traveller that _Salix fragilis_
L., and _Scrophularia frigida_ Boiss., likewise yield in Persia
saccharine exudations. A kind of manna was anciently collected from the
cedar, _Pinus Cedrus_ L.[1530] Manna is yielded in Spain by _Cistus
ladaniferus_ L.[1531] _Australian Manna_, which is in small rounded,
opaque, white, dry masses, is found on the leaves of _Eucalyptus
viminalis_ Labill. It contains a kind of sugar called _Melitose_,[1532]
has a sweet thistle, is devoid of medicinal properties and is not
collected for use.[1533]
[1527] Further particulars, see Flückiger, _Ueber die Eichenmanna von
Kurdistan_, in _Archiv der Pharmacie_, 200 (1872) 159.
[1528] _Loc. cit._ p. 35.
[1529] Hanbury, _Science Papers_, p. 438.
[1530] Geoffroy, _Mat. Med._ ii. (1741) 584.
[1531] Dillon, _Travels through Spain_ (1780) p. 127.
[1532] Gmelin, _Chemistry_, xv. 296.
[1533] _Pharm. Journ._ iv. (1863) 108.
The substance named _Tigala_ (corrupted into _Trehala_), from which a
peculiar sugar has been obtained,[1534] is the coccoon of a beetle, and
not properly a saccharine exudation.[1535]
The _Lerp Manna_ of Australia is also of animal origin.[1536] It
consists of water 14, white thread-like portion 33, sugar 53 parts.
The threads possess some of the characteristic properties of starch,
from which they differ entirely by their form and unalterability even
in boiling water. Yet in sealed tubes, they dissolve in 30 parts of
water at 135° C. The sugar is dextrogyre; it impregnates the threads
as a soft brown amorphous mass. In the purified state it does not
crystallize, even after a long time. By means of dilute sulphuric acid,
the threads are converted into crystalline grape sugar.