BARK. 
of a deep green colour, very tender and suc- 
culent. When viewed with a microscope, 
it seems to be composed of fibres which 
cross each other in every direction, like the 
fibres which compose a net. Both in it and 
the epidermis there are numberless inter- 
stices, which have been compared to so 
many small bladders. The cortical layers 
form the innermost part of the bark, or that 
which is next to the wood. They consist of 
several thin membranes, lying the one 
above the other; and their number ap- 
pears to increase with the age of the plant. 
Each of these layers is composed of longi- 
tudinal fibres, which separate and approach 
each other alternately, so as to form a kind 
of net-work. The meshes of this net-work 
correspond in each of the layers ; and they 
become smaller and smaller in every layer 
as it approaches the wood. These meshes 
are filled with a green-coloured cellular sub- 
stance, which has been compared by anato- 
mists to a number of bladders adhering 
together, and communicating with each 
other. 
The matter of the parenchyma, and the 
juices which exist in barks, vary extremely, 
and probably occasion most of the dif- 
ferences between them. Some, as oak bark, 
are characterized by their astringency, and 
contain tannin ; others, as cinnamon, are 
aromatic, and contain an essential oil; others 
are bitter, as Jesuits bark ; some are chiefly 
mucilaginous, others resinous, &c. 
1. Bark of the cinchona floribunda, or 
quinquina of St. Domingo. This bark is 
in rolled pieces, six or seven inches long, 
and three or four lines in thickness. Its 
colour is greyish green externally, but 
within it exhibits different shades of green, 
purple, white, brown, &c. Its taste is bit- 
ter and disagreeable ; its odour strong and 
unpleasant. It gives out nearly half its 
weight to water, provided it be boiled in a 
sufficient quantity of that liquid. The re- 
sidue possesses the properties of woody 
fibre. The decoction of the bark has a 
reddish brown colour, and an extremely 
bitter taste. It deposits on cooling a 
blackish substance, soft and tenacious, which 
does not dissolve in cold water, though it is 
soluble in hot water and in alcohol. More 
of this substance precipitates as the liquor 
is evapprated. When the inspissated juice, 
freed from this precipitate, is mixed with 
alcohol, a quantity of gummy matter sepa- 
rates. When the black matter which pre- 
cipitates as the decoction cools, is treated 
with hot alcohol, the greatest part of it is 
dissolved ; but a fine red powder remains 
mixed with some mucilage, which is easily 
separated by water. When the alcoholic 
solution is exposed to the air, it deposits 
light yellowish crystals of a saline nature. 
When mixed with water, white flakes are 
thrown down, which possess the properties 
of gluten ; but the greatest part remains in 
solution. Thus the soluble part of the bark 
may be separated into five distinct sub- 
stances ; namely, gum, gluten, a red pow- 
der, a saline matter, and a brownish bitter 
substance, retained in solution by the di- 
luted alcohol. The last is by far the most 
abundant. To it the peculiar qualities of 
the decoction of this bark are to be as- 
cribed. 
2. Bark of cinchona officinalis. This 
tree grows in Quito ; it is confined to the. 
high grounds, and when stripped of its bark 
soon dies. There are three different kinds 
of bark to be found in commerce, but whe- 
ther they be all obtained from the same 
trees is not known ; the contrary is proba- 
ble. The following are the most remark- 
able of these varieties. Red Peruvian bark. 
— This bark is usually in large pieces, and is 
reducible to powder with more ease than 
the preceding. Its powder is reddish brown, 
and has a slightly bitter taste, with a good 
deal of astringency. Yellow Peruvian 
bark. — This species of bark, first brought 
into use in this country about the year 1790, 
has not yet been subjected to a rigorous 
analysis ; but its constituents do not ap- 
pear, from the trials which have been made, 
to differ much from those of the red spe- 
cies. Pale Peruvian bark. — This is the 
common variety of the bark. It has not 
yet been subjected to a correct chemical 
analysis. Its taste is astringent and bitter, 
and very disagreeable. It is supposed to 
contain a bitter principle, tannin, extractive, 
and resin. Besides these, it contains a 
principle first pointed out by Seguin, and 
upon which Dr. Duncan, junior, published 
some experiments. It is distinguished by 
the property of precipitating infusion of 
galls ; but as this property is, common to a 
considerable number of substances, it is not 
sufficient alone to characterize it. 
3. Bark of cinchona caribaea. — This bark 
was first made known by Dr. Wright, who 
published a botanical description of the 
tree, with a figure, in the Philosophical 
Transactions, vol. 67, and an account of 
the medicinal properties of the bark in the 
London Medical Journal for 1787. A descrip- 
tion of a tree to which the same name is given, 
