The effect of wind is such that an imperceptible air current may have a very pronounced influence. Rubner3 has shown that wind becomes perceptible when it attains a velocity of 0.4 to 0.5 meter a second, and that if a wind much below this threshold value, having a velocity of 0.18 meter per second, act upon the exposed area of the arm, there is an increased neat loss of between 19 and 75 per cent., depending on the temperature of the wind, above what would be lost were the air quiet.

The effect of wind of moderate humidity and different temperatures on the metabolism of a man clad in summer clothes, as compared with the metabolism during atmospheric calm, is shown in Wolpert's4 experiment below:

1 Freund and Marchand: "Archiv fur exp. Path, und Pharm.," 1913, lxxiii, 276.

2 Schapals: "Zeitschrift fur exp. Path, und Ther.," 1912, x, 222. 3 Rubner: "Archiv fur Hygiene," 1904, 1, 296.

4 Wolpert: "Ibid., 1898, xxxiii, 206.

Influence Of Wind On Metabolism In Man

According to this, a breeze having a temperature of 150 to 200 and moving at the rate of about 15 miles per hour (8 meters per second) has a greater effect upon the metabolism of a man clad in summer clothing than a temperature of 20 would have during perfect* atmospheric quiet. In all the experiments the smallest amount of carbon dioxid is eliminated between 300 and 400.

The above experiments were performed on a thin man, and it will be noticed that there was no rise in his metabolism at a temperature of between 350 and 400. Rubner explains this as due to the sufficiency of the evaporation of perspiration on the surface for the cooling of the organism.

A fat man, however, with a thick, ill-conducting layer of adipose tissue is not so immune to the effect of high temperatures upon his metabolism. This is especially pronounced in a damp climate. Thus Rubner1 obtains the following results from a fat man wearing clothes:

1 Rubner: "Energiegesetze," 1902, pp. 208, 232.

Influence Of Temperature And Humidity On The Metabolism Of A Fat Man

* Body temperature rose 0.1°. † Body temperature rose 0.0°.

‡ Body temperature rose 0.40. § Body temperature rose o.o°.

The fact that in the experiment where there was 30 per cent, humidity the metabolism largely increased at 360 to 370 without concomitant rise in body temperature leads Rubner to theorize that there must have been an overheating of the cells where the metabolism was progressing, even though this might not have been determinable by the clinical thermometer.

It appears that on a hot, humid day the metabolism of a fat individual may be 50 per cent, higher than on a day of moderate temperature and the same humidity. The whole of the body heat is lost through the evaporation of water which is here hindered by the humidity. There is a large and exhausting excretion of sweat which on account of the difficulty in evaporation is not effective in cooling the body. At a moderate temperature, where the greater part of the heat loss is by radiation and conduction, the excretion of water is not excessive.

Lee1 gives the following table which shows the influence of varying temperatures and humidities upon the body temperatures of a group of normal men:

1 Lee: Proceedings of the Soc. for Ex. Biol, and Med., 1915, xii, 72.

There can be no doubt that climatic conditions modify racial characteristics. The emigrant from northern Europe, living upon a farm in the hot and often moist climate of an American summer, must restrict his layer of adipose tissue if he is to live comfortably. The same holds true in Italy. The difference between John Bull and Uncle Sam seems to be one of climatic adaptation. On the contrary, the Eskimo cultivates a thick, fat layer to protect himself from frost. It is also interesting to note that prostrations from the heat appear in New York with 66 per cent, humidity and a temperature of 31.5° (2.30 p. m., August 24, 1905). Rubner1 says that a lightly clad thin man, at a temperature of 300 with humidity at 65 per cent., bore the effect so badly that he feared to raise the temperature to 350. This individual had readily tolerated 350 in dry air.

The maximum mortality from "summer troubles" in children in New York coincides with the first great wave of heat accompanied by humidity which falls upon the city. Similar climatic conditions at later dates are not so fatal. It may be that the fatality of these intestinal affections is due to the inefficiency of the apparatus for the physical discharge of heat in the infant organism. It is also possible that infection may be more readily brought about under these conditions (p. 344).