PHYSIOLOGICAL EFFECTS.
Some of the relations of water to the living system have been considered in the preceding section. In the present connection we shall consider chiefly those effects resulting from the application of water to the human body in various ways which give to it its value as a remedial agent, though its therapeutical applications will be deferred to succeeding sections.
The effects of water upon the human system are the results of the operation of its physical properties in conjunction with the vital forces. As with all other agents, its effects may be either local, or general, according to the mode of application. Different effects are also produced according as the administration is internal or external. Many other modifying circumstances, as age, sex, and physical condition, affect the results in a greater or lesser degree.
Water affects the system through three different means; viz.:—
1. As a diluent;
2. By its solvent properties;
3. By modifying the general or local temperature of the body.
1. Water as a Diluent.—Water is received into the system by absorption, either through a mucousmembrane, 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 ofurea, 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:—
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 ofthe 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 afterthe 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 beaccuratelydetermined 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 thearterioles, 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 lessenedwith the blood, the amount of heatproducedis 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 applyingit 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 fromthe 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 thesurface 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;
2. Increased vital and chemical action increases the production of heat;
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 stimulanteffects 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 thenatural 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 thewarmbath.
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 extensivea 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.