According to Dragendorff (1878) _mucilaginous matters_ occur in the
different varieties of rhubarb to the amount of from 11 to 17 per
cent. He states them to consist of mucilage (properly so called),
arabic acid, metarabic acid and pararabin, and moreover enumerates also
pectose among the constituents of the drug.
Small quantities of albuminoid substances, malic acid, fat and sugar
have also been met with in rhubarb. As to its mineral constituents,
their amount is exceedingly variable. Two samples of good China Rhubarb
dried at 100° C. and incinerated, yielded us respectively 12·9 and
13·87 per cent. of ash. Another sample, which we had particularly
selected on account of its pale tint, afforded no less than 43·27 per
cent. of ash. The ash consists of carbonates of calcium and potassium.
English rhubarb from Banbury (portions of a large specimen) left after
incineration 10·90 per cent. of ash.
From a practical point of view the chemical history of rhubarb is far
from satisfactory, for we are still ignorant to what principle the drug
owes its therapeutic value, or what are the pharmaceutical preparations
in which the active matter may be most appropriately exhibited.
Chrysophan is said to act as a purgative, but less powerfully than
rhubarb itself.
=Uses=—Rhubarb is one of the commonest and most valuable purgatives; it
is also taken as a stomachic and tonic.
=Substitutes=—These are found in the roots of the various species of
_Rheum_ cultivated in Europe. In most countries, the cultivation of
rhubarb for medicinal use has at some time been attempted. Yet in but
few instances has it been persistently carried on; and though the drug
produced has often been of good appearance, it has failed to gain
the confidence of medical men, and to acquire much importance in the
drug-market. The European rhubarb most interesting from our point of
view is
_English Rhubarb_—So early as 1535, Andrew Boorde, an English
Carthusian monk and practitioner of medicine, obtained seeds of
rhubarb, which he sent as “_a grett tresure_” to Sir Thomas Cromwell,
Secretary of State to Henry VIII.; but as he says they “_come
owtt of barbary_” we must be allowed to hold their genuineness as
doubtful.[1841]
In the following century, namely about the year 1608, Prosper Alpinus
of Padua cultivated as the True Rhubarb a plant which is now known as
_Rheum Rhaponticum_ L., a native of Southern Siberia and the regions
of the Volga.[1842] From this stock, Sir Matthew Lister, physician
to Charles I., procured seeds when in Italy, and gave them to
Parkinson,[1843] who raised plants from them.
[1841] Boorde’s _Introduction and Dyetary_, reprinted by the Early
English Text Society, 1870. 56.
[1842] Prosper Alpinus, _De Rhapontico_, Lugd. Bat. 1718.
[1843] _Theatrum Botanicum_, 1640. 157.
Collinson obtained rhubarb plants from seeds procured in Tartary, and
sent to him in 1742 by Professor Siegesbeck of St. Petersburg.[1844]
About 1777 Hayward, an apothecary of Banbury in Oxfordshire, commenced
the cultivation of rhubarb with plants of _Rh. Rhaponticum_, raised
from seeds sent from Russia in 1762. The drug he produced was so good
that the Society of Arts awarded him in 1789 a silver medal, and in
1794 a gold medal.[1845] The Society also awarded medals about the same
time (1789-1793) to growers of rhubarb in Somersetshire, Yorkshire, and
Middlesex, some of whom, it appears, cultivated _Rh. palmatum_. On the
death of Hayward in 1811, his rhubarb plants came into the possession
of Mr. P. Usher, by whose descendants, Mr. R. Usher and sons, they are
still cultivated at Bodicott, a village near Banbury.
The authors of this book had the pleasure of inspecting the rhubarb
fields of Messrs. Usher on Sept. 4, 1872, and of seeing the whole
process of preparing the root for the market.[1846] The land under
cultivation is about 17 acres, the soil being a rich friable loam.
The roots are taken from the ground during the autumn up to the month
of November. It is considered advantageous that they should be 6 or
7 years old, but they are seldom allowed to attain more than 3 or 4
years. The clumps of root as removed from the field to the yard, where
the trimming takes place, are of huge size, weighing with the earth
attached to them as much as 60 or 70 lb. They are partially cleaned,
the smaller roots are cut off, and the large central portion is rapidly
trimmed into a short, cylindrical mass the size of a child’s head.
This latter subsequently undergoes a still further paring, and is
finally sliced longitudinally; the other and less valuable roots are
also pared, trimmed, and assorted according to size. The fresh roots
are fleshy, easily cut, and of a beautiful deep yellow. All are dried
in buildings constructed for the purpose, and heated by flues. The
drying occupies several weeks. The root after drying has a shrivelled,
unsightly appearance, which may be remedied by paring and filing. The
finished drug has to be stored in a warm dry place.
When well prepared, Banbury rhubarb is of excellent appearance. The
finest pieces, which are semi-cylindrical, are quite equal in size to
the drug of China. The colour is as good, and the fractured surface
exhibits pink markings not less distinct and brilliant. Even the
smaller roots, which are dried as sticks, have internally a good
colour, and afford a fine powder. But the odour is somewhat different
from that of Chinese rhubarb; the taste is less bitter but more
mucilaginous and astringent, and the root is of a more spongy, soft,
and brittle texture. The structure is the same as that of the Chinese
rhubarb, except that, as already stated, the star-like spots, if
present, are isolated, and not arranged in a regular zone.
The drug commands but a low price, and is chiefly sold, it is said,
for exportation in the state of powder. It is not easily purchased in
London.
[1844] Dillwyn, _Hortus Collinsonianus_, 1843. 45.
[1845] _Trans. of Soc. of Arts_, viii. (1790) 75; xii. (1794) 225.
[1846] No use is made of the leaves.—Some further particulars are given
by Holmes, _Pharm. Journal_, vii. (1877) 1017.
_French and German Rhubarb_—The cultivation of rhubarb was commenced
in France in the latter half of the last century, and has been pursued
with some enthusiasm in various localities. The species grown were
_Rheum palmatum_ L., _Rh. undulatum_ L., _Rh. compactum_ L., and _Rh.
Rhaponticum_ L. The first was thought by Guibourt[1847] to afford a
root more nearly approaching than any other the rhubarb of China; but
it is that which is cultivated the least readily, the central root
being liable to premature decay. Both this plant and _Rh. undulatum_
were formerly cultivated by order of the Russian Government on a large
scale at Kolywan and Krasnojarsk in Southern Siberia, but the culture
has, we believe, been long abandoned.[1848]
As to France, it appears from inquiries we have lately made (1873),
that except in the neighbourhood of Avignon and in a few other
scattered localities, the cultivation has now ceased.
_Rheum Rhaponticum_ is the source of the rhubarb which is produced
at Austerlitz and Auspitz in Moravia, and at Ilmitz, Kremnitz and
Frauenkirchen in Hungary. Some rhubarb is also produced in Silesia from
_Rh. Emodi_ Wall. (_Rh. australe_ Don.).