3. The body absorbs heat from the surrounding medium as any other colder
object would do.
In the general application of hot water or vapor, effects similar to its
local effects are produced upon the whole surface of the body,
involving, also, to a considerable extent, the deeper structures. The
pulse is accelerated because the small arteries are distended and more
active, creating a demand for a greater quantity of blood, requiring an
increase in the heart’s action. It is also quite probable that the
action of the heart is somewhat quickened as the result of the influence
of heat upon the pneumogastric nerve which controls it.
The cerebral symptoms, faintness, etc., which occur when heat is applied
in excess, are the result of the diversion of so large a proportion of
the blood into the superficial vessels. A prolonged hot foot bath or leg
bath will often produce faintness.
There are few agents which will so rapidly produce such powerfully
excitant and stimulant effects as the hot bath. The painful and
undesirable results occasioned by its incautious use are evidences of
its power.
_The Warm Bath._—In this connection we apply the term warm to baths of a
temperature between 85° and 98° F., though baths of a temperature
between 85° and 92° would be more accurately termed tepid, which term is
applied to baths of that temperature elsewhere than in this immediate
connection.
The warm bath never exceeds the temperature of the body, and is usually
below it. Its effect is uniformly to diminish the frequency of the pulse
and of respiration, and to decrease animal heat. Its effects are the
same as those of the cool or cold bath, in this respect, but they differ
in several other particulars. Unlike the cold bath, the warm bath is not
accompanied by an unpleasant shock, or chill, and, hence, is not
followed by reaction. It promotes the action of the skin in a very
marked degree, increasing both perspiration and absorption. When
continued for an hour or two, the weight is appreciably increased by the
absorption of water. Its general effects are very mild and soothing,
often inclining the patient to sleep.
This bath seems to produce its effects not so much by exciting the vital
energies to abnormal action or resistance, as by supplying the most
favorable conditions for the performance of the natural and usual
functions. This is doubtless on account of its close approximation to
the temperature of the body. In this respect, if this supposition be
true, it differs from baths of a temperature either much above or
greatly below the normal temperature of the body.
The warm vapor bath produces effects quite analogous to those of the
warm water bath. Its effect upon the processes of perspiration and
absorption is a little more marked, even with the same degree of
temperature. The results differ somewhat, according as the whole body is
enveloped, so that the warm vapor is taken into the lungs, or the head
excluded. A more equable effect is produced by including the whole body
in the bath, and no harm can result if the temperature is not raised
above that of the body, as it should not be, in the _warm_ bath.
=Sympathetic Effects.=—There is scarcely room for doubt that many of the
effects of the various kinds of water applications are wholly of a
sympathetic character. All portions of the body are intimately
associated together by a system of nerves called the sympathetic system,
from their peculiar function. Certain portions, as the skin and mucous
membrane, are particularly related. The large number of sensitive nerves
which connect the skin with the brain, bring it in peculiarly close
relations to that organ, and give additional potency to any agent
applied to so extensive a surface. The well-known fact that burns of the
skin are often the occasion of fatal ulceration of the mucous membrane
of the intestines sufficiently attests the intimate relation between
these two tissues; while the effects upon the skin of mental emotions,
as of shame and of fear, are conclusive evidence of the peculiar
closeness of relation between the cerebral and cutaneous organs. The
condition of the mind has much to do with the effect of a bath.
=Modes of Administration.=—There are numerous modes of administering
baths of all temperatures, each of which produces some modification of
the general effect of the given temperature. For example, such baths as
the douche, the spray, and the shower bath, are much more cooling in
their effects than a full bath at the same temperature; since, in the
latter case, nearly the whole body would be submerged in a medium of
equable temperature, while in the case of the spray, etc., the body
would be additionally cooled by the rapid evaporation taking place upon
its surface. Many other peculiar effects are obtained by particular
modes of administration, which will be described in their proper place.