pedestrian walks 32,000 meters a day, without a load, the energy expended, assuming him to weigh 70 kilograms, is 32,000 X 70=2,240,000 kilogram-meters. Haughton divides the work performed into "fatigue work," the effort necessary to carry the weight of the body, and "useful work," the energy expended in performing labor. For instance, Coulomb observed that the work done by porters employed to carry goods 2000 meters, returning unloaded, amounted to 348 kilograms in six journeys, or 58 kilograms at a time. The useful work performed was, therefore, 2000 X 348=696,000 kilogrammeters; the fatigue work was 2000 X 2 X 70 X 6 = 1,680,000 kilogram-meters. This allows 70 kilograms as the weight of the porter, and takes into consideration that the body is carried in both directions, or 4000 meters. The total energy expended was 2,376,000 kilogrammeters. He also found that pedlars, who always travelled loaded with their packs, were able, with a load of 44 kilograms, to travel 19,000 meters per day. Assuming their weight of 70 kilograms, we find―

In athletic exercises it is essential that the amount of energy expended be carefully determined, in order to ascertain whether the exercise is likely to prove beneficial or otherwise. The amount of energy expended in athletic sports should not exceed that expended by laborers in hard manual labor. In athletic contests, of course, the energy expended is often in excess of this amount; but a period of comparative rest must follow the contest, in order to allow the body to recuperate from the fatigue

induced by the contest. The harmful effects of the large amount of energy expended in some athletic contests is frequently seen when these contests take place at too short intervals, allowing insufficient time for the contestants to recover from the fatigue of the previous contest. The same effects are also noted in soldiers who are compelled to make frequent forced marches over long distances.

From what has been learned of the effects of exercise, it will be seen that athletic training should aim to increase the breathing-power; to strengthen the power of the heart's action; to make the muscular action more vigorous and enduring; and to decrease the amount of fat. These results are obtained by careful dieting; by regular and systematic exercise; and by increasing the action of the eliminating organs, especially the skin.

CHAPTER IX.

CLOTHING.

THE function of clothing is to protect against the weather-heat, cold, and dampness-and to protect against injury. All other uses of clothing have no direct hygienic interest, only indirectly in so far as they may be injurious to health.

Protection against Cold.-The most important use of clothing in cold climates is to protect against cold. Clothing serves this purpose by diminishing the radiation of heat from the body. The radiation of heat from the body diminishes with the number of layers of clothing worn, and is also dependent upon the nature of the clothing worn. If we take the amount of radiation of heat from the naked body as 100, the radiation is reduced to 73 by means of a woollen shirt; to 60 by means of both a woollen and a linen shirt; to 46 by means of a woollen and a linen shirt and a vest; to 33 by the addition of a coat. Rubner found that if the radiation at 15° C. is taken as 100, at 23° C. it is only 69, at 29° C. it is 56, and at 32° C. it is 31.

The radiation of heat is directly dependent upon the thickness of the layer of clothing. If we take the loss of heat as 100, a thickness of 1 millimeter of cotton allows a radiation of 77 per cent.; 2 millimeters, of 68 per cent.; 3 millimeters, of 65 per cent.; 4 millimeters, of 57 per cent.; 5 millimeters, of 53 per cent.; 10 millimeters, of 41 per cent.; 15 millimeters, of 30 per cent.

The thickness of clothing, in our climate, must not be so great as to increase perceptibly the air-pressure by compression, nor so thin as to decrease perceptibly the air-pressure. The thickness of the clothing is, therefore,

are

one of the most important features. The radiation of heat from the body is very nearly the same whatever the nature of the clothing. Wool, silk, and cotton equally warm when thickness of the layer is the same. The most rational clothing, however, is that which conserves the heat of the body with the least quantity of material. Flannel would be the lightest and warmest; but, since it wears so rapidly, woollen cloth is more serviceable, because it wears better. The smoothly woven cloths are not so warm as the tricot cloths, but they are more serviceable.

The clothing should not only be light, but it should functionate well with regard to the absorption of moisture from the skin. It should take up the moisture as readily as possible, and should quickly dry out. For this reason the clothing worn next the body should be porous, so that all the pores may not be filled with perspiration. Closely woven goods is not adapted for this purpose. Some authorities claim that linen, of coarse mesh, is best adapted for this purpose because it does not retain the moisture as long as wool.

Protection against Heat.-The degree of porosity is an important feature in summer clothing. The color of summer clothing is also important. Dark clothing absorbs heat to some extent, and in consequence it is somewhat warmer than white fabrics or those of lighter colors. The degree of porosity is, however, the most important factor, because on this property depends the interchange of air through the skin. The effect of the direct radiation of heat from the sun may be inhibited in part by a proper covering of the head. For this purpose straw hats with broad brims are most serviceable. They shade the head and face, and allow free ventilation of the scalp, with a layer of air between the head and the covering. This is important, because air is a poor conductor of heat. Protection against Dampness. During rainy weather the use of some impervious material serves to exclude the dampness from the body and clothing. Damp

clothing is injurious not only because it is liable to produce chill, but because it prevents the free evaporation of heat and moisture from the surface of the body. The importance of keeping the clothing dry in rainy weather is therefore self-evident.

Protection against Injury.-Clothing protects the body against mechanical injury, from frost, or from the direct rays of the sun. Among civilized peoples protection of the feet is also necessary to avoid injury or annoyance in walking over rough ground. The sole of the shoe should conform to the shape of the foot. This

FIG. 46. Correct sole
(Hueppe).

FIG. 47.-Shoemaker's
sole (Hueppe).

is of the greatest importance. The length of the sole is the so-called Meyer line (Fig. 46, ab), which extends from the middle of the heel through the middle of the great toe, and lies parallel with the inner border of the anterior half of the foot. The breadth of the sole is indicated by the Starck line (Fig. 46, cd), which extends diagonally from the head of the first metatarsal bone to form the letter V. The shoemaker's sole is usually cut so that the shoe is symmetrically divided right and left by a line extending through the middle, and which commonly corresponds to the anatomical axis (Fig. 47). As the result