Warm-blooded Animals (Homeotherms)

In humans and other mammals, temperature regulation represents the balance between heat production from metabolic sources and heat loss from evaporation (perspiration) and the processes of radiation, convection, and conduction. In a cold environment, body heat is conserved first by constriction of blood vessels near the body surface and later by waves of muscle contractions, or shivering, which serve to increase metabolism. Shivering can result in a maximum fivefold increase in metabolism. Below about 40°F; (4°C;) a naked person cannot sufficiently increase the metabolic rate to replace heat lost to the environment. Another heat-conserving mechanism, goose bumps, or piloerection, raises the body hairs; although not especially effective in humans, in animals it increases the thickness of the insulating fur or feather layer.

In a warm environment, heat must be dissipated to maintain body temperature. In humans, increased surface blood flow, especially to the limbs, acts to dissipate heat at the surface. At environmental temperatures above 93°F; (34°C;), or at lower temperatures when metabolism has been increased by work, heat must be lost through the evaporation of the water in sweat. People in active work may lose as much as 4 quarts per hour for short periods. However, when the temperature and humidity are both high, evaporation is slowed, and sweating is not effective. Most mammals do not have sweat glands but keep cool by panting (evaporation through the respiratory tract) and by increased salivation and skin and fur licking.

Temperature regulatory mechanisms act through the autonomic nervous system and are largely controlled by the hypothalamus of the brain, which responds to stimuli from nerve receptors in the skin. Continued exposure to heat or cold results in some slow acclimatization, e.g., more active sweating in response to continued heat and an increase in subcutaneous fat deposits in response to continued cold.

Environmental extremes may result in failure to maintain normal body temperature. In both increased body temperature, or hyperthermia, and decreased body temperature, or hypothermia, death may result (see heat exhaustion). Controlled hypothermia is used in some types of surgery to temporarily decrease the metabolic rate. Fever, caused by a resetting of the temperature regulatory mechanism, is a response to fever-causing, or pyrogenic, substances, such as bacterial endotoxins or leucocyte extracts. The upper limit of body temperature compatible with survival is about 107°F; (42°C;), while the lower limit varies.

In humans the inner body temperature alternates in daily activity cycles; it is usually lowest in early morning and is slightly higher at the late afternoon peak. In human females there is also a monthly temperature variation related to the ovulatory cycle. In many mammals and birds the body temperature shows more pronounced cyclic variations than in humans. For example, in hibernators the body temperature may lower to only a few degrees above the environmental temperature during the dormant periods; mammalian hibernators reawake spontaneously and in their active period are homeothermic.

Cold-blooded Animals (Poikilotherms)

Reptiles and other poikilothermic animals bask in warm weather and must hibernate in winter. The body temperature of fishes must remain close to that of the surrounding water, because heat is lost directly into the water during respiration; however, in some fishes, such as the bluefin tuna, a special network of fine veins and arteries called the rete mirabile provides a thermal barrier against loss of metabolic heat. The mechanism of temperature regulation in homeotherms is considered an important evolutionary advance in that physical activity in such animals can be relatively independent of the environment.

Endocrine gland in the brain that produces melatonin. It is large in children and begins to shrink at puberty. The gland may play a significant role in sexual maturation, circadian rhythm and sleep induction, and seasonal affective disorder and depression. In animals it is known to play a major role in sexual development, hibernation, and seasonal breeding.

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Metaphysical problem of the relationship between mind and body. The modern problem stems from the thought of René Descartes, who is responsible for the classical formulation of dualism. Descartes's interactionism had many critics even in his own day. Thomas Hobbes denied the existence of mental substance. Materialism of a sort was also supported by Descartes's correspondent Pierre Gassendi (1592–1655). Benedict de Spinoza posited a single substance of which the mental and the material are attributes; his theory is known as psycho-physical parallelism. More recent views include the double-aspect theory, identity theory, eliminative materialism (which denies the reality of the familiar categories of mental state posited in so-called folk psychology), and theories of supervenience.

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Intentional alteration of the human body for religious, aesthetic, or social reasons. Modifications and mutilations are performed for purposes such as magical protection, medical or pseudo-medical intervention, cosmetic enhancement, and punishment. Alterations include head flattening, insertion of a lip plug, tattoos, scarification, piercing of the ear and other parts of the body, circumcision, foot binding, and amputation. That similar modifications are interpreted very differently from one culture to the next is an excellent indication of the relativity of ideals of beauty and deformity.

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Opaque watercolour. Also known as poster paint, designer's colour, and body colour, it differs from transparent watercolour in that the pigments are bound by liquid glue, which is used as a thinner. The addition of white pigment lightens the tone and lends opacity. Gouache paints dry to a matte finish and, if desired, without visible brush marks. They can be applied thinly or thickly. A wide range of colours are available, including fluorescent and metallic pigments. The suede finish and crisp lines characteristic of many Indian and Islamic miniature paintings is produced by this medium; it is used in Western screen and fan decoration and was used by modern artists such as Georges Rouault and Paul Klee.

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(born May 16, 1832, Stockbridge, N.Y., U.S.—died Jan. 6, 1901, Chicago, Ill.) U.S. entrepreneur and innovator. Armour's first entrepreneurial success was in California mining endeavours. He vastly expanded his family's Midwestern grain and meatpacking business in 1875, originating the use of byproducts and the sale of canned meat. When railcar refrigeration was introduced in the 1880s (see Gustavus Franklin Swift), he established distributing plants in eastern states and began exporting Armour meat products to Europe. His Armour & Co. enterprises helped make Chicago the meatpacking capital of the world.

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Theoretical surface that absorbs all radiant energy that falls on it, and radiates electromagnetic energy at all frequencies, from radio waves to gamma rays, with an intensity distribution dependent on its temperature. Because all visible light falling on such a surface is absorbed without reflection, the surface will appear black as long as its temperature is such that its emission peak is not in the visible portion of the spectrum. Seealso absorption.

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