motion, the expenditure of sensorial power is for a while lessened, but not
its general production in the brain, nor its derivation into the
weakly-stimulated part. Hence in strong people, or such whose fibres abound
with sensorial power, if the first tribe of an associate train of motions
be deprived in part of its accustomed stimulus, its action becomes
diminished; and the sensorial power becomes accumulated, and by its
superabundance, or overflowing as it were, increases the action of the
second tribe of the associate actions by reverse sympathy. As exposing the
warm skin for a moderate time to cold air increases the action of the
stomach, and thus strengthens the power of digestion.

On the reverse, when additional stimulus within certain limits is partially
applied to parts, which are deficient in respect to the natural quantity of
sensorial power, the expenditure of sensorial power is increased, but in a
less degree than the increased production of it in the brain, or its
increased derivation into the strongly-stimulated organ. Hence in weak
people, or such whose fibres are deficient of sensorial power, if the first
tribe of an associate train of motions be subjected for a while to greater
stimulus than usual, a greater production of sensorial power, or a greater
derivation of it into the stimulated parts occurs; which by its excess, or
overflowing as it were, increases the actions of the second tribe of the
associate motions by direct sympathy. Thus when vomiting occurs with cold
extremities, a blister on the back in a few hours occasions universal
warmth of the skin, and stops the vomiting. And when a diarrhoea occurs
with pale skin and cold extremities, the pricking of the points of a
flannel shirt, worn next the skin, occasions universal warmth of it, and
checks or cures the diarrhoea.

In some associate trains of action nevertheless reverse sympathies more
frequently occur than direct ones, and in others direct ones more
frequently than reverse ones. Thus in continued fever with debility there
appears to be a reverse sympathy between the capillary vessels of the
stomach and those of the skin; because there exists a total aversion to
solid food, and constant heat on the surface of the body. Yet these two
systems of vessels are at other times actuated by direct sympathy, as when
paleness attends sickness, or cold feet induces indigestion. This subject
requires to be further investigated, as it probably depends