In the three preceding articles of this series an excellent physiological basis for an understanding of the principles of hydrotherapy has been outlined. With a clear and definite comprehension of these principles, it will be much easier to understand how certain and definite results can be produced by the scientific application of hydrotherapy.
Water as a therapeutic agent owes its value, in addition to its universal distribution and ready accessibility, to three distinct physical properties, as follows:—
Its ability to communicate heat to the body, and to abstract heat from the body.
Its solvent properties.
Its ready conversion from a liquid to a solid or gaseous condition.
To consider these properties a little more in detail, it may be said that a pound of water is capable of absorbing more heat than a pound of any other substance. For example, a pound of water is capable of absorbing five times as much heat as an equal weight of glass; about ten times as much as the same weight of iron, zinc, copper, or brass, and thirty times as much as the same quantity of lead.
Water is also a fairly good conductor of heat. It is much better, for example, than air. It is for this reason that the application of water feels hotter or colder than air at the same temperature coming in contact with the body.
The solvent properties of water is an important consideration. Water is the medium by which the foods are transferred to the various parts of the body. Food taken into the alimentary canal in solid form is first dissolved in the process of digestion; is absorbed and carried in liquid form to different portions of the body, and is again converted into solid material, such as muscle, bone, nerves, etc., where it thus remains until it has served its purpose, when it is again dissolved, and as tissue waste, it is carried in solution to the various excretory organs of the body, and eliminated.
Water is used as a remedial measure in liquid form chiefly, but frequently in the form of ice; hence the third physical property renders it of special value. Steam, as such, is practically never used, owing to its extremely high temperature, which would destroy the tissues. The vapor of condensation from steam is useful in certain conditions, in the form of a Russian bath, for inhalation, etc.
The result produced from any application of water depends, first of all, upon the temperature which is used. The range of temperature varies from 32° to 140°. Temperatures above this point are sometimes used, principally for the checking of hemorrhage, when it is possible to use a temperature of 160°. For the sake of convenience, the following classification of the temperatures may be given: Very cold, 32° to 55°; cold, 55° to 65°; cool, 65° to 80°; tepid, 80° to 92°; neutral, 92° to 95°; warm, 92° to 98°; hot, 98° to 104°; very hot, 104° and above.
As water at different temperatures produces such widely differing results, it is essential that exact temperatures should be determined. This, of course, is a simple matter, with an ordinary thermometer ready at hand. A thermometer is not, however, absolutely essential, as it is possible, within reasonable limits, to secure the temperature desired, by using given quantities of water at known temperatures. For example, the boiling point of water is 212° F. at sea level. Deep well water remains practically at a temperature of 53° the year round. Knowing these temperatures, by simple calculation it is an easy matter to secure water at almost any desired temperature; for instance, two quarts of deep well water and one quart of boiling water would equal three quarts of water at a temperature of 106° (53 × 2 + 212 = 318 ÷ 3 = 106). Two and one half quarts of water at 53° and one quart of boiling water equals 98°. This might be carried out to almost any desired degree. The cold water should be placed in the vessel first, as the hot water, if put in first, would rapidly lose its heat. It should be borne in mind that the boiling point of water varies according to the altitude. There is practically a difference of 2° for every one thousand feet. The effect of a given application, in addition to the temperature, depends upon the duration of the procedure and the mode of application.
A very large proportion of the applications of water made to the surface of the body depend for their efficiency upon the fact that the skin is connected by means of nerves with the interior of the body, as mentioned in the preceding studies. Through the mechanism of these nerve filaments it is possible to produce the same result upon an internal organ as is produced upon the surface of the body where the application is made. The result thus produced is designated as a reflex effect.
When water is applied to the body in the form of a spray or douche, or accompanied by friction or percussion, there is an additional influence exerted by means of the impact of the water or hand upon the skin, which is known as a mechanical effect. Hence the result produced is the sum of the reflex and mechanical effects. In general, the predominance of either of these effects depends upon the area involved in the application; for example, if the area is small, the reflex effect will predominate. If an ice bag is applied over the region of the stomach, it will cause the blood vessels both of the skin and of the stomach to contract, greatly lessening the amount of blood in both areas; but if the application be general, such as a cold immersion bath, there will be a general contraction of the blood vessels of the skin, which will cause a displacement inward of so large a quantity of blood that the blood vessels of the internal parts will be mechanically dilated, and thus the reflex effect of cold is quickly overcome by the mechanical effect or fluxion of blood to the internal parts of the body.
For a clear understanding of the subject, it will be necessary to obtain a more complete knowledge of the distinct physiological effects of cold and heat. Cold is a vital depressant. This is its primary effect under all conditions, and in all methods of application. Cold lessens cell activity. As illustrations of this may be mentioned the common use of a refrigerator for the preservation of food. The cold prevents the growth and multiplication of germs. If the ameba, a single cell organism, be observed carefully under the microscope, it will be noted that its activity is greatly diminished, and practically ceases, when cold is applied, but that it quickly revives and becomes very active when heat is applied.
The effect of cold upon the skin is to produce, first, a pallor or coldness of the skin, due to contraction of the small blood vessels. If the application is long continued, the surface becomes blue. This is the so-called primary effect of the cold. When the application is withdrawn, if it has not been too greatly prolonged, the pallor or blueness of the skin quickly gives place to redness, which is the secondary effect of the cold. We thus have a primary, or action, effect, and a secondary, or reaction, effect.
Another effect produced by a cold application to the skin is a decreased or entirely suspended perspiratory activity. General perspiration may be checked by a mere local application of cold, as, for example, immersing the feet or the hands in cold water will cause immediate suspension of general perspiration. This sudden checking of perspiration by the application of cold is injurious only when the body is in a state of fatigue, or when the perspiratory activity is the result of an effort on the part of the system to antagonize high fever, as in typhoid, malaria, and other diseases.
Cold slows the circulation, and diminishes the frequency of the heart-beat. The contraction of the surface vessels, resulting from cold application, lessens the amount of blood in the skin, and consequently the elimination of heat through the skin is greatly diminished. In the reaction which occurs, following a short application of cold, the blood vessels of the skin dilate, and the pallor gives way to redness; heat is eliminated from the body more rapidly, and the perspiratory activity may be renewed.
The body recognizes cold as an enemy, and sets in operation such mechanisms as will counteract the depressing influence of the cold upon its cell activity. It is to this arousing of the bodily activities to resist the influence of cold that the beneficial results of cold applications are due. This point will be elaborated more fully later in speaking of the tonic effects of cold. It might at first seem a contradiction to speak of cold as being always a depressant, and then to mention its tonic effects, but these results will be apparent when it is recognized that following a cold application there are two effects; a primary and a secondary, or an action and a reaction, effect. In its primary, or action, effect cold is a depressant, but in the reaction an exciting or stimulating effect is apparent. The tendency to reaction from cold diminishes as the application is prolonged. Too prolonged an application of cold entirely prevents reaction, and results in the destruction of tissue. Freezing of the extremities from too long exposure is an example of this effect. As before mentioned, the primary, or action, effect of cold is to produce a contraction of the small blood vessels of the skin, with mechanical dilatation of the internal vessels when the application is general. In the reaction there is dilatation of the blood vessels of the surface, with contraction of the internal vessels.
Again: the cold first produces pallor, with goose-flesh appearance and roughness of the skin, also a sensation of chilliness, trembling, shivering; but in the reaction these give way to a redness of the skin, the skin becomes soft and smooth, and there is a sensation of warmth, comfort, and well-being.
Prolonged cold lessens the activity of the muscles, which is well illustrated in the stiffness and clumsiness of the fingers as the result of exposure to a low temperature.
Goose flesh is caused by the stimulation of the involuntary muscles of the skin as a result of the cold application.
Shivering is an effort on the part of nature to produce an excessive quantity of heat to compensate for the increased loss of heat, and is due to the involuntary action of the voluntary muscles. Shivering occurs as soon as the bodily temperature begins to lower as the result of an application of cold.
Nearly all the phenomena arising from applications of cold water are illustrations of the effect of cold upon the nervous system, whereby the special effects are produced in various organs.
In the reaction from a short application of cold to the head there is an increase in brain activity. A prolonged application of intense cold to the head decidedly lessens brain activity, and if continued for a sufficiently long period, results in drowsiness, or even absolute unconsciousness. For centuries a knowledge of this has been made of practical use in prisons, for subduing refractory prisoners, by pouring cold water upon the head for a considerable length of time.