Another factor in the heat regulation of man is clothes. Certain savage races living in cool climates do without clothes, as, for example, aborigines of Terra del Fuego, who, according to the reports of travelers, substituted a covering of oil. In such races the process of "hardening" or the development of the physical regulation must be carried to a maximum. In civilized countries man endeavors to remove all the influence of chemical regulation by keeping his skin covered. Only about 20 per cent, of his surface is normally exposed to the air. The most important constituent of clothes is the air, which is a much worse conductor of heat than is the fiber. This is especially true of furs (p. 136). Thickness of the cloth will give a greater layer of air and will prevent heat loss from the body. A densely woven cloth prevents proper ventilation and does not absorb moisture. In hot weather a porous cloth next to the skin which can absorb moisture and permit its ready evaporation is of high importance. If a garment worn next to the skin becomes thoroughly wet the evaporation of sweat at a high temperature is largely prevented, to the great discomfort of the individual, while at a lower temperature heat loss through conduction is greatly facilitated, with a sensation of chill. Two experiments cited by Rubner1 indicate the effect of clothes on metabolism. An individual was kept at a temperature of between ii° and 12º and wore different clothes at different times. His carbon dioxid and water excretion were as follows:

1 Rubner: "Energiegesetze," 1902, p. 232.

Influence Of Clothes On Metabolism In Man At A Temperature Of 11° To 12°

When the man was comfortable the chemical regulation of temperature was eliminated.

Rubner remarks that while the radiant energy of the sun is large in quantity, he has been unable to find any influence upon a man under ordinary circumstances, but believes that it may take the place of heat produced through chemical regulation on cold days. Thus a person living in the high altitude of Davos, Switzerland, feels "much more comfortable in the sun on a cold day than he does in the shade. However, Zuntz while living on the summit of Monte Rosa found that sunlight did not reduce metabolism (p. 429).

1 Rubner: "Energiegesetze," 1902, p. 225.

Hasselbalch4 found that if the naked body of a man was strongly exposed to ultra-violet rays the rate of respiration was diminished while the depth was increased. The skin was red with dilated capillaries and the blood-pressure fell. Lind-hard, in 1910, showed there is a yearly periodicity of the respiratory rate in the Arctic region, it being less in the spring and summer than in the winter. The enormous variations in the chemical intensity of the sun's rays in the Arctic region are undoubtedly the cause of this manifestation. Even in Copenhagen the same phenomenon has been observed by Hasselbalch and Lindhard.2 The volume of respiration increases 26 per cent, in the summer. The intensity of the metabolic processes are not affected. This accords with the fact that there is no change in metabolism through an alter-tion of the respiratory rhythm induced by cutting the pulmonary branches of the vagus.3

Durig and Zuntz4 find that the climate of the seashore does not influence the basal metabolism, nor does travel to the Canary Islands in the tropics,5 nor the condition of sea-sickness.

The fundamental heat production in the organism is not reduced by liberating heat from electric energy within the organism.6 Thus, although high frequency currents equal to 1.8 amperes and 176 volts were passed through the body during two and one-half hours under conditions such as avoided high concentration, and though heat was produced thereby which was equal to three to four times the energy requirement of the time, yet there was in fact a slight increase in the oxidative processes of the subjects attributable to hyperthermia, sweating, increased pulse, and respiratory activity.

1 Hasselbalch: "Skan. Archiv f. Physiol.," 1905, xvii, 431. 2 Hasselbalch and Lindhard: "Skan. Arch. f. Physiol.," 1911, xxv, 361; Ibid., 1912, xxvi, 221.

3 Rauber and Voit: " Sitzungsber. der baeyerischen Akademie," 1868.

4 Durig and Zuntz: "Biochemische Zeitschrift," 1912, xxxix, 422; Ibid., P 435.

5 For an interesting discussion of the offects of tropical light on white men read C. E. Woodruff, "Medical Ethnology," New York, 1915.

6 Durig and Grau: "Biochemische Zeitschrift," 1912-13, xlviii, 480.

Extraneous heat, therefore, will not replace the chemical energy of the food-stuffs in maintaining the life processes.

In what follows it will be shown that the ingestion of food may add to the heat production of the organism and diminish the necessity of heat production through chemical regulation in cold weather. Also it may very uncomfortably increase the production of heat and perspiration in warm weather, especially if protein be largely taken (p. 247).

From this chapter the influence of climate is seen to be noteworthy. It explains why a temperature of - 400 may be comfortably borne in winter, in the Adirondack Mountains, for example, if the air be dry and still; why a much warmer atmosphere which is damp and windy may "cut to the bone" with cold; why a hot, dry climate may be entirely comfortable, when air at the same temperature laden with moisture may strike down many fatally and oppress every one; and how the effect of heat may be modified by the breezes and baths at the seashore. It does not explain the effect of the dry sirocco wind which blows from the Desert of Sahara, the universal depressant action of which has been attributed to unknown cosmic influences.