oportion, the heart and
arteries act with less energy than in their natural state. See Sect. XII.
1. 4.

That this quick small pulse is owing to want of irritability, appears,
first, because it attends other symptoms of want of irritability; and,
secondly, because on the application of a stimulus greater than usual, it
becomes slower and larger. Thus in cold fits of agues, in hysteric
palpitations of the heart, and when the body is much exhausted by
haemorrhages, or by fatigue, as well as in nervous fevers, the pulse becomes
quick and small; and secondly, in all those cases if an increase of
stimulus be added, by giving a little wine or opium; the quick small pulse
becomes slower and larger, as any one may easily experience on himself, by
counting his pulse after drinking one or two glasses of wine, when he is
faint from hunger or fatigue.

Now nothing can so strongly evince that this quick small pulse is owing to
defect of irritability, than that an additional stimulus, above what is
natural, makes it become slower and larger immediately: for what is meant
by a defect of irritability, but that the arteries and heart are not
excited into their usual exertions by their usual quantity of stimulus? but
if you increase the quantity of stimulus, and they immediately act with
their usual energy, this proves their previous want of their natural degree
of irritability. Thus the trembling hands of drunkards in a morning become
steady, and acquire strength to perform their usual offices, by the
accustomed stimulus of a glass or two of brandy.

2. In sleep and in apoplexy the pulse becomes slower, which is not owing to
defect of irritability, for it is at the same time larger; and thence the
quantity of the circulation is rather increased than diminished. In these
cases the organs of sense are closed, and the voluntary power is suspended,
while the motions dependent on internal irritations, as those of digestion
and secretion, are carried on with more than their usual vigour; which has
led superficial observers to confound these cases with those arising from
want of irritability. Thus if you lift up the eyelid of an apoplectic
patient, who is not actually dying, the iris will, as usual, contract
itself, as this motion is associated with the stimulus of light; but it is
not so in the last stages of nervous fevers, where the pupil of the eye
continues expanded in the broad day-light: in the former case there is a
want of voluntary