IL
P
A R
Of Irritability.
SECT.
L
ALTHOUGH many of the parts compofing* the human body
are endowed with a confiderable degree of elaflicity, where¬
by they reftore themfelves when over-flretched ; yet mufcular fi¬
bres alone at*e poflefled of a peculiar contractile power, which they
exert in confequence either of an effort of the will, or of fome
ftimulus applied to them or their nerves : by the former, voluntary
motion is produced \ by the latter involuntary *. The illuftrious
M. de Haller, who calls the contractile power of irritated mufcles
by the name of Irritability, has, by a variety of curious experi¬
ments upon living animals, {hewn, that it is a property of all muf
cular fibres ; and that no part, which is not mufcular, is irritable,
although, of the mufcular parts, fome are more and others lefs
fenfibie of irritation. But when, in his enumeration of the parts
of the body that are or are not irritable, he allows irritability to
the laCteal veins, mucous glands, and finufes, and yet denies it
wholely to the kidneys and ureters,, and alrnofl wholely to the ar¬
teries, veins, and excretory du&s of the glands, we cannot help
differing from him : fince thefe lafl parts are, at leaft, as much
mufcular as the former ; and fince his own experiments on living
and dying animals fhew neither the one nor the other to be ir¬
ritable f.
TH at the fmall arteries are not without irritability, may be de-
monflrated by experiments. Thus, when an acrid cataplafm i&
applied to the fkin, or fpirit of wine to the eye, whence proceeds the
inflammation which is foon produced in the fkin, and alrnofl in-*
* Vid, an EfTay on the vitaî motions, éc. fed. i. and 10;
t Ad. Göttingenf. vol. 2. p. 139,-143.