imitate each other in the kind as well as
in the quantity of their action; but it is difficult to distinguish them
from the associations of motions treated of in Section XXXV. Where the
actions of other persons are imitated there can be no doubt, or where we
imitate a preconceived idea by exertion of our locomotive muscles, as in
painting a dragon; all these imitations may aptly be referred to the
sources above described of the propensity to activity, and the facility of
repetition; at the same time I do not affirm, that all those other apparent
sensitive and irritative imitations may not be resolvable into associations
of a peculiar kind, in which certain distant parts of similar irritability
or sensibility, and which have habitually acted together, may affect each
other exactly with the same kinds of motion; as many parts are known to
sympathise in the quantity of their motions. And that therefore they may be
ultimately resolvable into associations of action, as described in Sect.
XXXV.

* * * * *

SECT. XXIII.

OF THE CIRCULATORY SYSTEM.

I. _The heart and arteries have no antagonist muscles. Veins absorb the
blood, propel it forwards, and distend the heart; contraction of the
heart distends the arteries. Vena portarum._ II. _Glands which take
their fluids from the blood. With long necks, with short necks._ III.
_Absorbent system._ IV. _Heat given out from glandular secretions.
Blood changes colour in the lungs and in the glands and capillaries._
V. _Blood is absorbed by veins, as chyle by lacteal vessels, otherwise
they could not join their streams._ VI. _Two kinds of stimulus,
agreeable and disagreeable. Glandular appetency. Glands originally
possessed sensation._

I. We now step forwards to illustrate some of the phenomena of diseases,
and to trace out their most efficacious methods of cure; and shall commence
this subject with a short description of the circulatory system.

As the nerves, whose extremities form our various organs of sense and
muscles, are all joined, or communicate, by means of the brain, for the
convenience perhaps of the distribution of a subtile ethereal fluid for the
purpose of motion; so all those vessels of the body, which carry the
grosser fluids for the purposes of nutrition, communicate with each other
by the heart.

The heart and arteries are hollow muscles, and are therefore indued with
power of contraction