avoided, yet a certain variation of stimulus seems to prolong the
excitability of the system; as during any diminution of the usual
quantity of stimulus, an accumulation of sensorial power is produced;
and in consequence the excitability, which was lessened by the action
of habitual stimulus, becomes restored. Thus those, who are uniformly
habituated to much artificial heat, as in warm parlours in the winter
months, lose their irritability in some degree, and become feeble like
hot-house plants; but by frequently going for a time into the cold
air, the sensorial power of irritability is accumulated and they
become stronger.

Whence it may be deduced, that the variations of the cold and heat of
this climate contribute to strengthen its inhabitants, who are more
active and vigorous, and live longer, than those of either much warmer
or much colder latitudes.

This accumulation of sensorial power from diminution of stimulus any
one may observe, who in severe weather may sit by the fire-side till
he is chill and uneasy with the sensation of cold; but if he walks
into the frosty air for a few minutes, an accumulation of sensorial
power is produced by diminution of the stimulus of heat, and on his
returning into the room where he was chill before, his whole skin will
now glow with warmth.

Hence it may be concluded, that the variations of the quantity of
stimuli within certain limits contribute to our health; and that those
houses which are kept too uniformly warm, are less wholesome than
where the inhabitants are occasionally exposed to cold air in passing
from one room to another.

Nevertheless to those weak habits with pale skins and large pupils of
the eyes, whose degree of irritability is less than health requires,
as in scrofulous, hysterical, and some consumptive constitutions, a
climate warmer than our own may be of service, as a greater stimulus
of heat may be wanted to excite their less irritability. And also a
more uniform quantity of heat may be serviceable to consumptive
patients than is met with in this country, as the lungs cannot be
clothed like the external skin, and are therefore subject to greater
extremes of heat and cold in passing in winter from a warm room into
the frosty air.

4. It should nevertheless be observed, that there is one kind of
stimulus, which though it be employed in quantity beyond its usual
state, seems to increase the production of sensorial power beyond the
expenditure of it (