=1. Water as a Diluent.=—Water is received into the system by
absorption, either through a mucous membrane, or through the skin. It
usually enters through the medium of the stomach and intestinal canal.
When received into the blood, it of course increases its volume, and
produces an increased fullness of the circulatory vessels, which are
never distended to their fullest extent, and hence allow room for change
in the volume of their contents. The blood is necessarily rendered more
fluid, and if previously in any degree viscid, its circulation is
quickened by its dilution.
=2. The Effects of the Solvent Properties of Water.=—With the exception
of air, water is the most transient of all the elements received into
the body. It is eliminated by the skin, the lungs, the kidneys, and the
intestines. By its solvent action, it dissolves the various poisonous
products of the disintegration of the tissues. The volume of the blood
being increased, more water comes in contact with the debris contained
in any part, and, in consequence, the same undesirable products are more
perfectly removed. The increased amount of excrementitious matter in
solution is brought in contact with the various depurating organs,
producing, notably, the following results:—
a. _An increase of the urinary excretion._ It is an important fact that
this increase does not consist in the addition of water merely, or
dilution, but that there is also an increased amount of _urea_, the
chief excrementitious principle removed from the blood by the kidneys.
b. _An increase in the cutaneous excretion._ Water-drinking is one of
the most efficient means of producing copious perspiration, which, as
with the urinary excretion, is not a mere elimination of water, but is a
real depurating process.
c. _Increased action of the intestinal mucous membrane._ Elimination
from the mucous membrane of the intestinal track, which is an important
organ of excretion, is also increased by drinking freely of pure water.
The result of this increased action is not only to remove from the blood
some of its foulest constituents, but to render more fluid the contents
of the intestines, and thus tend to obviate that almost universal
accompaniment of sedentary habits, constipation.
The removal of clogging matters from the system in this manner allows
greater freedom of vital action, so that the activities of the body are
quickened, and both waste and repair, disintegration and assimilation,
are accelerated.
The use of water thus hastens all the vital processes by increasing the
change of tissue. This result is of course chiefly obtained by employing
it as a drink. The experiments of Liebig fully confirm this view. He
expressly mentions the free use of water as one of the means of
accelerating vital change. Prof. John B. Biddle, M. D., in his “Materia
Medica,” states that “it promotes both the metamorphosis and
construction of tissue,” from which fact he attributes to it valuable
curative properties, as an alterative, when the removal of a morbid
taint is desired, as in certain venereal diseases.
=3. Effects resulting from the Modification of Temperature.=—Perhaps the
most important, certainly the most common, effects of water upon the
living organism are those which result from its modifications of the
temperature of the body in its various modes of application. These
effects vary greatly according to the temperature, and the duration of
the application. General and local applications also differ in their
results.
It should be remarked that all of the effects of water are really the
results of the vital resistance of the system in its attempts to remove
abnormal or unusual conditions, or to accommodate itself to new
circumstances.
Baths are divided into six classes, according to their temperature, as
follows:—
1. Cold, 33° to 60° F.
2. Cool, 60° „ 70°
3. Temperate, 70° „ 85°
4. Tepid, 85° „ 92°
5. Warm, 92° „ 98°
6. Hot, 98° „ 112°
For the sake of simplicity, we will consider the effects of water
applications under three heads; viz., cold, warm, and hot.
_The Cold Bath._—Under this head we will consider applications of all
temperatures below 85° F. Cold or cool water, applied to any portion of
the body, causes instant contraction of the small arteries of the part,
through its influence upon the sympathetic or vasomotor system of
nerves. So long as the application of the unusual temperature is
continued, the vascular contraction is maintained, and the part seems
nearly bloodless. If the cold is below 33° F., and is long continued,
destruction of the tissues, by freezing, will result.
If a moderately cool or cold temperature is maintained for some time,
the blood-vessels of the part are more or less permanently contracted,
and the blood supply thus lessened. If, on the other hand, the
application is very brief, the contraction of the vessels is only
momentary, and is followed by a proportionate degree of relaxation, and
a corresponding increase in the supply of blood to the part.
A very cold bath applied to any considerable portion of the body, and
continued more than a very brief time, produces headache, dullness,
sometimes nausea and vomiting, loss of sensibility, and other unpleasant
and painful symptoms.
It is thus seen that the effects of cold are quite different—exactly
opposite, in fact—as the application is a prolonged, or a brief one. The
long application produces effects in some degree permanently sedative,
while the brief application is followed by a momentary condition which
may be termed shock, and which is usually followed very quickly by a
reaction analogous to stimulation when produced in any other manner.
_Effect of Cold upon the Pulse._—The experiments of Drs. Currie, Bell,
and others, show conclusively that the cold bath has the uniform effect
of diminishing the frequency of the heart’s action from ten to twenty
beats in a minute below the usual standard. Upon the first application
of cold, there is a slight increase in the rate of pulsation; but this
soon subsides, and is succeeded by a marked diminution. The ultimate
effect is the same, whether the application is made at its maximum
degree of severity or not; but if the application is first warm, being
gradually reduced in temperature, the result is reached without the
occurrence of the unpleasant shock, or feeling of chilliness, which
attends the sudden application of cold, especially in persons of
delicate nervous sensibilities. The amount and after duration of the
diminished rate of pulsation depends upon the temperature and duration
of the bath. In health, it does not commonly extend beyond a few hours
at most.
_Effect of Cold upon Temperature._—It was also shown by the same
experimenters that the temperature of the body is reduced
proportionately with the action of the heart. The natural temperature,
as shown by a thermometer placed in the axilla, is 98° F. During and
after a cold bath, the thermometer applied to the same part, indicates
from one-half a degree to five or six, or even more, degrees, diminution
of temperature. In some cases the temperature continues to fall after
the bath. The real temperature is lessened even though the skin may
glow, and may seem to possess increased warmth. Cold and heat are,
within certain limits, wholly relative terms to the nerves of
sensibility. What is warm at one time may be cold at another, though the
temperature remains the same. The same temperature may be warm to one
hand and cool to the other. Temperature can only be _accurately_
determined by the thermometer.
_Rationale of Effects of the Cold Bath._—The manner in which the cold
bath produces the sedative effects noted, is apparently simple. When
applied locally, to a single organ or part, it diminishes the
circulation in the part by occasioning contraction of the muscular coats
of the _arterioles_, or small arteries. Their caliber being thus
lessened, they of course allow the passage of less blood, and the
circulation in the part is diminished. There are, then, three causes for
the decrease of heat; viz.,—
1. A portion of the heat of any part is brought to it by the blood; the
supply of blood being lessened, the heat is diminished;
2. Heat is produced by vital or chemical changes which occur in the
capillaries or their immediate vicinity. These depend chiefly upon the
supply of oxygen, which, again, is largely regulated by the blood
supply; and it being lessened with the blood, the amount of heat
_produced_ is diminished.
3. The water in contact with the part, being of a lower temperature,
abstracts heat from it as it would from any other body of a higher
temperature than itself.
When the application of cold water is more general, being made to the
whole body, or to a considerable portion of it, the same effects are
produced on a larger scale. A large proportion of the small arteries of
the body, being brought under the influence of cold, are made to
contract, thus directly lessening the circulation, and so diminishing,
also, the production of heat. Through the sympathetic system, the same
effect produced upon the small arteries is produced also upon the heart,
lessening the rapidity of its contractions. Again, it has been
satisfactorily shown that the action of the heart is largely controlled
by the action of the small arteries; so that we have abundant
explanation of the decrease in the rate of pulsation. Finally, we have a
cold fluid in contact with a large portion of the body, abstracting heat
by conduction, as well as lessening its production.
Thus we see that water, when applied at a proper temperature, is one of
the most powerful means of depressing the vital activities of the body,
diminishing circulation and animal heat as will no other agent. The
several modes for applying it are considered in another portion of this
work.
_The Hot Bath._—We shall include under this head applications of a
temperature above 98° F., the mean temperature of the body. As with the
cold bath, the effects differ greatly according as the application is
brief or prolonged. Local and general applications also differ in their
effects.
A brief local application causes an increase in the circulation of a
part which very closely resembles, perhaps is identical with, active
congestion. The small arteries are distended, and the vital activities
and heat of the part are increased. The several effects seem to be
little different from those resulting from the application of a mild
sinapism. The action of the vital instincts is defensive in both cases.
When applied to special organs, special effects are produced. For
instance, a hot fomentation applied to the head for a few minutes will
usually produce drowsiness by diversion of a portion of the blood supply
of the brain to the skull and scalp. Prolonged applications produce a
more or less permanent relaxation of the blood-vessels, and consequent
congestion.
A hot bath applied to the whole body, or a large portion of it, produces
an acceleration of the pulse and an increase of animal heat
proportionate to the temperature of the bath. A bath at 106° to 108° F.
will increase the pulse from the normal standard to one hundred or one
hundred and twenty beats in a minute, in a short time. A bath four or
five degrees hotter has been known to increase the pulse to more than
one hundred and fifty beats in a minute.
When a hot bath is prolonged, the face becomes flushed, and the whole
skin very red; the head aches; sight is sometimes dimmed; ringing in the
ears, faintness, a stinging pain in the skin, and intense desire to
urinate are symptoms which are often present. Copious perspiration and
intense congestion of the skin are constant effects. The cutaneous
congestion, from relaxation of the blood-vessels, is apt to continue to
exist after the bath, if it is greatly prolonged, to the serious injury
of the subject.
The effects of the vapor bath are essentially the same as those
described, though a somewhat higher degree of heat is tolerated without
injury. In the hot-air bath, a still higher heat is borne with impunity.
_Rationale of Effects of the Hot Bath._—It scarcely need be repeated
that all of the effects noticed, as well as those of all other baths,
are chiefly the results of modifications of vital action occasioned by
the agent employed. The application of heat to the body occasions
relaxation of the muscular coats of the small arteries, and increased
action of those vessels. No doubt this is for the purpose of bringing
moisture to the surface to protect the tissues against the unnatural
heat. As is the case with cold baths, the causes which modify the heat
are three; viz.,—
1. The increased quantity of blood circulating through the part brings
to it an increased amount of heat;