When the surrounding medium is hotter than the body, as in these hot-bath methods, radiation and convection are abolished, and consequently the only cooling mechanism left is sweating. But as the heat-regulating centers do not discriminate, the sweat continues to form so long as the body is hotter than normal, even though the conditions are such that the sweating cannot serve its usual purpose in cooling the body. Just so long, therefore, as there is a heightened body temperature the sweating continues, in a futile attempt of the heat-regulating mechanism to bring the body temperature to normal in the usual way.

In the methods for inducing diaphoresis it is this tendency of the sweating mechanism to respond to raised body heat of which advantage is taken. For so long as the sweat is prevented from accomplishing its object of cooling the body, the sweating will continue indefinitely. Hence the use of exercise, hot drinks, and hot-air and hot-water baths to increase the body heat; and of blankets, sweaters, etc., to lessen the heat radiation and to absorb the sweat and prevent its evaporation at the surface of. the body.

Fat

In a sense there is a protective garment about a fat person, the thick, poorly conducting layer of fat interfering with heat loss; so that if the internal temperature is raised, an excessive amount of sweat is poured out in the effort of the body to cool itself. On a hot, dry day a fat man may lose by evaporation as much as 3200 calories; on a hot, humid day a fat man sweats more profusely, yet suffers more from the heat than the thin man. If a fat person ingests no water while carrying out diaphoretic measures, the body tends to form water from the fat, and so lessen its adipose deposit. Von Noorden says that 100 grams of fat yield 107 grams of water, and he states that restriction of the water intake produces a loss of fat. But he quotes Heilner and also Henneberg as authorities for the statements that in experimental animals abundant water-drinking increases fat catabolism, and in stock-raising renders it very difficult to fatten animals. Hawk says that water increases protein metabolism. Yet by vigorous daily exercise, wearing heavy sweaters, limitation.

of the fluids, and regulation of the food ingested a fat man may lose 40 or 50 pounds of his weight in a few months and yet feel in splendid condition.

The Character Of The Sweat In Diaphoresis

The normal secretion of the sweat-glands is of low specific gravity and of faintly alkaline reaction, and there are various salts present. The slight acidity sometimes noted is due to admixture with the fatty acids of the sebaceous secretion. It is frequently stated that the copious sweat produced by methods to raise body heat is slightly alkaline, but in many tests by the author of the sweat of nephritics in the hot-pack it has been, without exception, acid.

The Relation Of Diaphoresis To Nitrogenous Excretion

The ordinary insensible perspiration does not contain any appreciable nitrogenous matter (Lusk). The average of many tests by different experimenters gives 0.068 gm. nitrogen per day in skin elimination.

Benedict (1906) got 0.071 gm. nitrogen per day in the whole cutaneous secretions, both sebaceous and sweat, of a resting man. "But when the sweat was increased, as in a man at moderate work, the nitrogen from the skin rose to 0.13 gm. per hour, and in a man at hard work to 0.22 gm. per hour. The nitrogen of these larger quantities represented urea, uric acid, creatinin, and other constituents of urine." Therefore, copious sweating from hard work, which Atwater and Benedict found might be eight times the normal sweating, represented the loss of 1 gm. of nitrogenous excreta in five hours. This shows that the sweat-glands of normal persons can, to some degree, be made to take on a function of the kidneys. But in this work there was greatly increased muscular activity, i. e., increased metabolism, and consequently the results are not indicative of the real excretory value of diaphoresis in sick people.

Some of the striking experiments on diaphoresis are worth noting:

Hoelscher, in 22 experiments with hot-air baths, obtained 6719 c..c. of sweat, containing a total nitrogen of 0.48 gm. per 1000 c.c. Eijkmann studied three medical students at light occupation in the climate of Java. In three hours he obtained 0.222 gm. nitrogen; in twenty-four hours, 0.761 and 1.362 gm. nitrogen.

Benedict experimented with a man twenty-four years old, 75 kilos in weight, at rest in the respiration chamber during four days of fasting and then three days with food. The average daily nitrogen excreted by the skin was 0.103 gm. When such a man did eight hours' work on a stationary bicycle in the respiratory calorimeter, his clothes extracted with distilled water gave an average of 0.29 gm. nitrogen per day for eighty-eight days' work.

Lavonius estimated that in a circus athlete the loss in the sweat was 1.8 gm. nitrogen per day. Zuntz calculated that the loss of nitrogen to the perspiration, including shed epithelium, is 0.46 gm. per day.

Atwater and Benedict with a professional bicyclist twenty-eight years of age and 62 kilos in weight, placed in the bicycle ergometer for four hours, found that the heat output was about 600 calories per hour, and that the total nitrogen increase in the sweat was roughly proportional to the work done.

In the sweat of 6 normal humans and 3 nephritics Riggs (1911) failed to find uric acid. But Plaggemeyer and Marshall (1914) tested normal passive sweat, obtained during 25 minutes of hot-air sweating, and filtered to eliminate shed epithelium, and found urea, uric acid, ammonia, and diastase as constant constituents, the urea being 0.05-0.3 per cent. and the uric acid 0.00005-0.00018 per cent. The total output of nitrogen ranged from 34 to 640 mg., the ratio of ammonia nitrogen to the total nitrogen being considerably higher than that in the urine.

In Sickness

In uremia, a condition of poisoning in which the molecular concentration of the blood is increased as a result of impaired kidneys, the sweat poured out may contain a much greater proportion of nitrogenous material than that from hard work. In fact, in nephritis crystals of urea have actually been found deposited upon the skin; though this was only in terminal conditions of collapse with abnormal capillary permeability. That in uremia profuse sweating is of great value in carrying off nitrogenous material was the contention of Bendix (1904), who claimed to be able, by profuse sweating alone, to bring to normal the greatly depressed freezing-point of the blood of uremic patients, i. e., to reduce its molecular concentration to normal. But Austin and Miller (1914) observed no effect from sweat-baths on the non-protein nitrogen of the blood in nephritics with hypertension.

Tachau (1912) gave one-hour sweat-baths to nephritics and determined that the nitrogen excreted amounted to 0.2 to 0.49 gm., while the chlorides were 1.31 to 2.05 gm. Von Noorden says that the perspiration of nephritics contains a maximum of 1 to 1.3 gm. of urea from profuse sweating, and this is too little to be of moment to the kidneys. Thus from an excretion point of view sweating in nephritis must be considered chiefly of use in removing water and perhaps chlorides rather than urea or other nitrogenous waste. But by draining the blood of water it has the additional effect of mobilizing the tissue fluids, of promoting the visceral circulation, and perhaps also of bringing into the blood antibodies to be utilized or toxins to be excreted. Hunt has demonstrated that normally the reserve of water in the body is so great that even when several liters of water have been lost by sweating, the percentage of water in the blood is not appreciably diminished because of supply from the tissue fluids. Moreover, the dilatation of the skin vessels results in a diversion of the blood from the congested internal organs.

In intestinal putrefactive toxemia with indicanuria, indol has been detected in the perspiration.

By the chlorides excreted Spitta has determined that sweating is as great in a hot bath as in hot air of the same temperature; therefore by a simple hot bath, as by the more elaborate baths, profuse sweating may be produced, and afterward may continue for many hours in excess of normal if the person remains in a warm room or in bed.

Therapeutics And Administration

1. To lower temperature, in mild fevers - the liquor ammonii acetatis, 2 drams (8 c.c.), or spiritus aetheris nitrosi, 1 dram (4 c.c.). The effect of these is probably almost nothing.

2. To overcome chill or cold - by relieving internal congestion and reestablishing proper cutaneous circulation. Hot lemonade at bedtime, whisky and hot water, Dover's powder, and a hot bath are the favorites, with extra bed-clothes. Dover's powder is in extensive use by both physicians and the laity to produce sweating, especially if there is pain or restlessness. But unless it is given with a copious hot drink and the patient uses extra bed-clothing, the chances of its producing profuse sweating are very small. It is given in 5 or 10-grain doses, and is often followed the next morning by nausea, headache, and a feeling of lassitude.

3. To lessen obesity - exercise with heavy woolen clothing, Turkish baths, hot baths, restriction of liquids ingested.

4. To assist the kidneys in the removal of accumulated poisons, as in uremia, and possibly in gout, rheumatoid conditions, eclampsia, and other toxemias. Hot-pack, vapor baths, etc., with or without pilocarpine, and, if there is no edema, with copious drafts of water. A hot-pack is often followed by a decided increase in kidney activity.

5. To lessen edema and promote the absorption of dropsical effusions - hot-pack, vapor baths, etc., with dry diet, very little water being ingested; sometimes with pilocarpine. It must be understood, of course, that dropsical fluid is reabsorbed from the tissue spaces when by sweating the blood loses water. An added factor in lessening edema may be the excretion of sodium chloride in the sweat.

6. To lessen congestion of the internal eye and of the middle and internal ear - especially by pilocarpine.

7. To hasten the outbreak 0/ the rash in measles and other exanthemata. Hot baths for this purpose are in common employment.

Local sweating with high temperature is used in chronic rheumatism, rheumatoid and gonorrheal arthritis, and other joint affections. In the ordinary baking-box for an arm or a leg, such as Bier's, the temperature can be borne for half an hour up to about 180o F., the heat of a baking oven, and this induces a marked hyperemia of the limb, with profuse perspiration. With the Sprague apparatus, in which, by a special arrangement, the evaporation of the perspiration keeps pace with its production so that there is never any visible perspiration, a temperature of 3000 to 3500 F., the so-called "superheated air," can be borne without discomfort or burning. At this temperature, if a drop of water should collect on the skin, it would instantly form steam and scald the skin. A limb, or even the whole body except the head, can be kept at this temperature for fifteen or twenty minutes, the body temperature rising from 1 to 4 degrees. Cold applications should be kept upon the head.