The essentials of healthA text-book of anatomy, physiology, hygiene, alcohol, and narcotics . s and their ducts : (1)ducts of the sweat glands ; (2) thehair shaft. inch. It is estimated that there are over three millionsof these glands in the entire skin. The Perspiration. The perspiration is a colorless fluid,secreted in the coils of the sweat glands. It is of verysimple composition, over per cent of it being inorganic substances, as sodic chloride, commonsalt, give it a salty taste; while some organic ingre-dients, as the fatty acids, impart to it an odor. Theperspiration is
The essentials of healthA text-book of anatomy, physiology, hygiene, alcohol, and narcotics . s and their ducts : (1)ducts of the sweat glands ; (2) thehair shaft. inch. It is estimated that there are over three millionsof these glands in the entire skin. The Perspiration. The perspiration is a colorless fluid,secreted in the coils of the sweat glands. It is of verysimple composition, over per cent of it being inorganic substances, as sodic chloride, commonsalt, give it a salty taste; while some organic ingre-dients, as the fatty acids, impart to it an odor. Theperspiration is a continuous secretion. When it is THE SKIN. 209 small in amount, the water is evaporated from the skinat once, therefore its presence on the skin is not no-ticed; this is called the insensible perspiration. As soonas the secretion is increased, it does not all evaporate,but gathers as drops of sweat on the surface; this is calledthe sensible perspiration. Many conditions cause theamount of perspiration to vary. In some individuals thewhole amount per day is very small; while in others it. Fig. 85. The surface of the skin, slightly magnified, showing theopenings of the sweat glands. is very large. It is a fair average for the year throughto say that from two to four pounds are secreted eachday. There is a marked difference in the perspiration ofthe lower animals ; the horse perspires freely ; the oxto a slight extent only ; and the dog but little, if panting of the dog after exercising allows muchwater to be given off from the body through the lungs; 14 210 THE ESSENTIALS OF HEALTH. and in this way the object of regulating the temperatureof the body is gained, as will be described later. Controlled by Nerves. The activity of the sweat glandsis under the control of certain nerves. While it is truethat dilatation of the blood vessels is usually associatedwith profuse perspiration, yet it is possible to arousethese glands into activity even after the supply of bloodhas bee
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