Reaction Value of Heat
One very great value of the application of heat to the surface of the body is that it increases the amount of heat in the skin. This in¬creases the ac¬tivity of the nerves and blood vessels in this part and prepares it to react more promptly and vigorously to cold applica¬tions. When the heat is ap¬plied generally (or to certain areas that under its stimulation may greatly influence the entire body, such as the spine, the abdomen,, or the feet), the entire body is prepared for quick reaction to cold applications or baths. Tims the hotter the preliminary applications, the colder the bath that may be taken with prompt and complete reaction—a fact that is contrary to the belief of most people. Circulation and Heat
Because of this heightened reactive power, the preliminary heating of the skin is of very great importance in many conditions, such as fatigue. rheumatism, neuralgia, anemia,- enfeeblement. and coldness of the skin from any cause.
Heat materially affects the circulation of the blood. The first effect of a full hot bath is to in¬crease the activity of the heart and produce con¬gestion of the internal organs, especially the brain. Such effects make it unwise to administer such a bath to plethoric or “full-blooded” indi¬viduals, or those who have even slight degrees of arterial hardening, or who have had a “stroke” of apoplexy. Those who are so affected by hot baths as to develop fullness and throbbing in the head should avoid them unless they have a cold compress about the throat or a cold turban about the head. Hot compresses uj>on the spine or the abdomen, hot sits-baths. and hot foot-baths also greatly stimulate the general circulation, as is indicated by the increase in perspiration often occurring during such applications and baths. Even hot hand baths will have this effect upon many people. Needless to say. such baths as the Russian and Turkish and the electric-cabinet bath all greatly stimulate the circulation.
The influence of heat upon the respiration is to produce easier and more frequent breathing, though the depth of respiratory movements is de¬creased. In other words, the amount of air breathed in and out is somewhat less than normal. Vapor baths (moist heat), especially, render the breathing easier and slightly increase the rate. But dry hot air, unless it is only moderately dry. will have an opposite effect. After a hot bath there is a temporarily diminished rate and depth of respiration. A very hot tub bath produces a sense of tightness in the chest, very similar to that produced by a cold bath.
It has been noted that the primary effect of cold is to dimin¬ish muscular irritability and capacity for muscular work. This is the effect also of prolonged hot applications. The weak¬ness following a long general bath is well known to most peo¬ple. It is due largely to the weakening of the muscles, or, rather, the reduced capacity of the muscles for response to stimuli.