thereof, or sinking in them, according to the Degree of Pressure ; and on taking away his
Hand, he could see it subside entirely into the little Bladder at the Bottom, and that as
plainly as he had ever seen Water ascend and descend in a Tube of Glass.
A Prickle thus pressed upon, and the Liquor rising in it, is represented by the Letter C.
Hence it is evident to a Demonstration, that the burning acute Pain, Swelling and In-
flammation that follow immediately on thrusting these Prickles into any Part of the Body ;
are owing to an Injection, at the same Instant, through the Cavities of these Prickles, of
a corrosive or poisonous Juice, lodged in Bags or Bladders at the Roots of the said Prickles,
and forced to ascend in them by their being pressed down on the said Bags or Bladders.
Such a Structure and Effect are exactly similar to the Sting of a Scorpion, Wasp, Bee,
&c. and the Consequence of being stung thereby. For the Sting of these Animals, like
the Thorn of a Nettle, is an exceeding sharp-pointed Tube, which entering the Skin or
Flesh serves to convey a poisonous Liquor into the Wound, that by irritating the nervous
and sensible Parts occasions all the ensuing Uneasiness and Mischief : And this Liquor, as
in the Nettle, is prepared and contained in a little Bag at the Root or Bottom of the Sting.
Nor is the Difference very great as to Vipers and other Serpents, whose Bite is dange-
rous ; for the Wounds their Teeth make would be very harmless, were they not hol-
low, and a Venom squirted through them into the Wounds they give.
D, D, D, D, &c. are a Kind of Thorns or Prickles without any visible Bladders of Li-
quor at their Roots, and a great deal smaller, as well as more numerous, than those that
have such Vessels. These probably may be no farther hurtful than to occasion a little
Itching.
E, E, a Sort of Pearl-like Globules, perfectly transparent, that are here and there in-
terspersed on both Sides the Leaf of this Plant, and grow to it much after the Manner as
Oak-Apples grow on the Leaves of an Oak.
F, F, F, the Ribs or large Sap-Canals, whence all the Prickles issue, and the Bladders
at their Roots are constantly supplied with the pungent Juices they contain.
g g g g g g, &c. are the intermediate and thinner Parts of the Leaf, which are almost
smooth, and afford little remarkable, but an irregular Ramification of very small Vessels or
Fibres.
PLATE XII. FIG. 2.
The Beard of a Wild-Oat
THE Beard of a Wild-Oat, cut asunder at the Ends A and B, is represented by the
two long prickly Figures we are now about to examine.
This little Production of Nature is wonderfully remarkable, on account of its making
an exceeding good Hygrometer, or Instrument for discovering the Dryness or Moisture of
the Air ; being extremely sensibly of, and visibly affected by the least Alteration as to those
Particulars. A Description of it must therefore be an instructive as well as entertaining
Amusement.
To the naked Eye it appears very inconsiderable, being only a small black or brown
Beard or Bristle, growing from the Side of the Inner-husk that covers the Grain of a
Wild-Oat. In “fuly and August, when the Grain is usually ripe and dry, this Beard is
bent somewhat below the Middle almost to a Right-Angle ; and the under and thicker
Part is writhed or twisted round down to the very Bottom, making three Revolutions in
some, in others more or less, according to the Bigness and Maturity of the Grain whereon
it grew, together with the Dryness or Moisture of the ambient Air. It is very brittle
when dry, and easily broken from the Husk from which it proceeds.
If it be put in Water, and viewed with a Magnifying-Glass, it seems like a twisted
Withe, having a Couple of Clefts or Channels along it ; the small bent Top will then
move round, the Under-Part untwist, and the Knee or Angle gradually become quite
strait, in which Condition, being at full Length, it extends sometimes to an Inch and an
half. When taken out of Water, and suffered to dry again, it by Degrees twists itself
round a it was before, and bends again near the Middle into its former Posture.
The Superficies of this little Body appears, by the Microscope, adorned with little Chan-
nels and interjacent Ridges, strait where the Beard is not twisted, but writhed where it is.
These Ridges are thickly beset on each side with Prickles, not unlike the Quills of Por-
cupines, (as are shewn by a a a a a) all the Points whereof are directed upwards towards
the Top of the Beard ; which is the Reason it sticks and grates against the Skin, if one
endeavours to draw it between the Figures the contrary Way. The Manner of growing,
Number, Closeness to each other, and Size of the Prickles, in proportion to the Beard, the
Figure will also shew.
