A diaphoretic is a remedy which tends to induce profuse sweating. Profuse sweating is diaphoresis.

The measures employed to produce diaphoresis are either drugs or methods of raising and keeping raised the body heat. We do not here consider terror, nausea, great weakness, and other causes of profuse sweating, as these are not therapeutic agents.

1. The drugs in common use are: pilocarpine, whisky, Dover's powder (pulvis ipecacuanhae et opii), the spirit of Mindererus (liquor ammonii acetatis), and the sweet spirit of niter (spiritus aetheris nitrosi), all of which we have already studied. Many other drugs tend to increase the sweat, but are not employed for that express purpose in therapeutics.

2. Methods of raising body heat and keeping it raised for diaphoretic purposes:

(a) Increasing the production of heat, as by exercise.

(b) Prevention of heat loss, as with blankets or extra bedclothes, or heavy woolen sweaters, as during exercise.

(c) The use of artificial heat, either internally or externally - internally, by hot drinks, and externally, by hot air, hot baths, vapor baths, electric baths, etc. A full Turkish bath involves remaining about five minutes in a room at 2300 F. (110° C), five minutes at 190°F. (87.8°C), and fifteen or twenty minutes at about 1400 F. (6o° C), the air being kept as dry as possible by good ventilation. A Russian bath is similar, but the air is surcharged with aqueous vapor by steam.

Water taken internally is both diaphoretic and diuretic. It is not cathartic (except perhaps in those who habitually under-drink), for the intestines can absorb such enormous quantities that, in normal conditions at least, the excess does not pass out by the rectum, but is excreted by the kidneys and skin (Starling). Cold water alone is essentially diuretic rather than diaphoretic, the sweat being increased to only a slight degree. But large drinks of hot water, as in the form of hot lemonade or chamomile tea, or large drinks of cold water plus measures which increase body heat and set in action the heat-regulating mechanism (as hot air, hot baths, exercise, etc.), result in a copious outpouring of sweat.

It is our custom in therapeutics to combine the measures. For example:

1. In exercising to remove fat a sweater or two is worn to prevent heat loss by evaporation of the sweat.

2. To check a cold, a liberal draft of hot lemonade or water at bed-time, with or without whisky, is assisted by extra bed-clothing, and sometimes a preliminary hot bath.

3. In nephritis and dropsical conditions the hot-pack or hot-air bath is employed, with sometimes, in addition, a hypodermatic of pilocarpine hydrochloride, 1/10 grain (0.006 gm.).

The hot-pack gives a combination of increased external heat with prevention of heat loss. In giving a hot-pack the patient, all except the head, is wrapped in a blanket or sheet (the arms being separated from the body by a layer of material), then successively in two blankets which have been wrung out of very hot water, then perhaps in a rubber sheet, with the bed-clothes over all. He is kept thus for from fifteen to thirty minutes. If the hot-pack is not for dropsy, a copious drink of water or lemonade may be administered; if it is for dropsy, liquid must not be given. To prevent headache, an ice-bag or wet cold cloth should be applied to the head. In dyspneic conditions the pack should not be extended high on the chest.

The electric bath, the hot-air bath, and the vapor bath are sometimes used for the same purposes. The electric bath is given in a cabinet in which the patient sits (head out), surrounded by electric lights. In the hot-air and vapor baths the patient, wrapped in a sheet, sits in a cabinet or tent with the head out; or if in bed, may have a sheet hung over him in the form of a tent. A heater in the tent or cabinet, or hot air conducted into the tent by a pipe, makes a hot-air bath; the steam from a kettle makes a vapor bath. Cold applications to the head during these baths tend to prevent headache.

By any of these methods copious sweating is produced, even to the amount of several quarts; and if the skin is not exposed to cold, the production of sweat may continue above normal for as much as twenty-four hours. If, however, sweating does not result, there may be headache and feelings of faintness, and even collapse, as sometimes occurs in the Turkish bath. Even when there is profuse sweating, collapse sometimes takes place in a hot-pack, and especially is this likely after pilocarpine; so in serious heart conditions, or if there is a tendency to edema of the lungs, diaphoretic measures must be used with caution. Nevertheless, as a rule, profuse sweating is not so exhausting as repeated catharsis.

During or immediately following a copious sweat, exposure to cold may result in chilling of the surface, with contraction of the skin vessels and internal congestion, i. e., a cold. Therefore, before going out after a heavy sweat one should have a cold sponge or shower with a good rubbing down of the skin and a short period of rest.

The Rationale Of Sweating

Normally, the loss of heat through the skin is due to radiation and convection from the surface of the body, and to the cooling effect of the evaporation of sweat. Radiation and convection are promoted by cold, and by dilatation of the skin vessels, as in exercise; but it is largely by sweating that the heat loss of the body is normally increased.

Ordinarily the evaporation of the sweat keeps pace with its production, so that the sweat does not gather into perceptible moisture. But when the sweat cannot evaporate as rapidly as it is produced, as during exercise, or in a humid atmosphere, or for other reasons, the perspiration collects and becomes visible. Perspiration that is visible indicates that the heat-regulating mechanism has overdone the production of sweat, and that more is produced than under the existing circumstances can be utilized for cooling purposes.