Applied biology : an elementary textbook and laboratory guide / by Maurice A. Bigelow and Anna N. Bigelow.

  • Maurice Bigelow
Date:
1911
Catalogue details

Licence: In copyright

Credit: Applied biology : an elementary textbook and laboratory guide / by Maurice A. Bigelow and Anna N. Bigelow. Source: Wellcome Collection.

    539/616 (page 523)
    The muscular system is the chief source of increased heat production, while the other organs probably generate the heat which is more or less constant, as during sleep or complete rest. When these organs are unable to supply the necessary heat, shivering, which is involuntary ac^tivity of muscles, may begin and thus increase the internal supply of heat. Loss of heat is partly by respiration. This is very impor- tant for dogs, which “ pant ” when overheated because their skin perspires little except on the pads of the feet. They also lose heat rapidly from the evaporation that occurs on the surface of the protruded tongue. Chickens are often seen breathing rapidly with the mouth open; and thus birds lose heat from their lungs and air-sacs. In man, however, the skin is the one great heat-regulator. The loss of heat from the human skin is controlled by nerves, some of which regulate (§ 414) the flow of blood to the skin and sweat-glands, and some stimulate these glands into activity. Rapid exercise causes the sweat-glands to become active. The effect of the sweat is illustrated by the familiar cooling of bottles of water wrapped with wet towels exposed to warm air; of water allowed to evaporate from the hands or face on a summer’s day; or of the porous water- jugs and canvas bags which the inhabitants of some hot countries use for their drinking water because the small amount^ of oozing water is evaporated and cools the water in the jug. We also know that following a bath on a hot day the body cools rapidly, and the explanation is that the heat of the skin was used to evaporate the water. Now, the sweat-glands are simply mechanisms for covering the skin with water ready for evaporation at all times when the skin is warmed by blood circulating rapidly. In addition to the heat lost by evaporation of water on the surface, there is much loss by radiation, es])ecially in cold weather when the skin gets warm after exercise which is not often active enough to cause moistening the skin with sweat.