A much higher temperature may be borne in dry air than in humid air, or that which is saturated with watery vapor. Thus, a shade temperature of 100° F. in the dry air of a high plain may be quite tolerable, while a temperature of 80° F. in the moisture-laden atmosphere of less elevated regions, is oppressive. The reason is that in dry air the sweat evaporates freely, and cools the skin. In saturated air at the bodily temperature there is little loss of heat by perspiration, or by evaporation from the bodily surface. This topic is again discussed in the description of the skin as a regulator of the bodily temperature (sec. 241). 227. Voluntary Means of Regulating the Temperature. The voluntary factor, as a means of regulating the heat loss in man, is one of great importance. Clothing retards the loss of heat by keeping in contact with it a layer of still air, which is an exceedingly bad conductor. When a man feels too warm and throws off his coat, he removes one of the badly conducting layers of air, and increases the heat loss by radiation and conduction. The vapor next the skin is thus allowed a freer access to the surface, and the loss of heat by evaporation of the sweat becomes greater. This voluntary factor by which the equilibrium is maintained must be regarded as of great importance. This power also exists in the lower animals, but to a much smaller extent. Thus a dog, on a hot day, runs out his tongue and stretches his limbs so as to increase the surface from which heat is radiated and conducted. The production, like the loss, of heat is to a certain extent under the control of the will. Work increases the production of heat, and rest, especially sleep, lessens it. Thus the inhabitants of very hot countries seek relief during the hottest part of the day by a siesta. The quantity and quality of food also influence the production of heat. A larger quantity of food is taken in winter than in summer. Among the inhabitants of the northern and Arctic regions, the daily consumption of food is far greater than in temperate and tropical climates. 228. Effect of Alcohol upon the Lungs. It is a well recognized fact that alcohol when taken into the stomach is carried from that organ to the liver, where, by the baneful directness of its presence, it produces a speedy and often disastrous effect. But the trail of its malign power does not disappear there. From the liver it passes to the right side of the heart, and thence to the lungs, where its influence is still for harm.