Other associate tribes and trains of motions, as well as the irritative and
sensitive ones, appear to be increased in their activity during the
suspension of volition in sleep. As those which contribute to circulate the
blood, and to perform the various secretions; as well as the associate
tribes and trains of ideas, which contribute to furnish the perpetual
dreams of our dreaming imaginations.

In sleep the secretions have generally been supposed to be diminished, as
the expectorated mucus in coughs, the fluids discharged in diarrhoeas, and
in salivation, except indeed the secretion of sweat, which is often visibly
increased. This error seems to have arisen from attention to the excretions
rather than to the secretions. For the secretions, except that of sweat,
are generally received into reservoirs, as the urine into the bladder, and
the mucus of the intestines and lungs into their respective cavities; but
these reservoirs do not exclude these fluids immediately by their stimulus,
but require at the same time some voluntary efforts, and therefore permit
them to remain during sleep. And as they thus continue longer in those
receptacles in our sleeping hours, a greater part is absorbed from them,
and the remainder becomes thicker, and sometimes in less quantity, though
at the time it was secreted the fluid was in greater quantity than in our
waking hours. Thus the urine is higher coloured after long sleep; which
shews that a greater quantity has been secreted, and that more of the
aqueous and saline part has been reabsorbed, and the earthy part left in
the bladder; hence thick urine in fevers shews only a greater action of the
vessels which secrete it in the kidneys, and of those which absorb it from
the bladder.

The same happens to the mucus expectorated in coughs, which is thus
thickened by absorption of its aqueous and saline parts; and the same of