What causes a fever?

Peter Nalin, a physician and associate professor of clinical family medicine and director of the family practice residency program at Indiana University, explains:

Fever—an elevated body temperature—is usually related to stimulation of the body's immune system. (Normal temperature fluctuates from about one degree below 98.6 degrees Fahrenheit to one degree above that number.)

Fever can support the immune system's attempt to gain advantage over infectious agents, and it makes the body less favorable as a host for replicating viruses and bacteria, which are temperature sensitive.

Infection is not the only cause, however. Amphetamine abuse and alcohol withdrawal can both elicit high temperatures, for example. And environmental stresses can also play a role in heatstroke and related illnesses.

The hypothalamus, which sits at the base of the brain, acts as the body's thermostat. It is triggered by floating biochemical substances called pyrogens, which flow through the bloodstream from sites where the immune system has identified potential trouble. Body tissue makes some pyrogens; many pathogens also produce them. When the hypothalamus detects the chemicals, it tells the body to generate more heat by increasing metabolism and to retain that warmth by reducing peripheral blood flow—thus producing a fever. Children typically get higher fevers that occur more readily, reflecting the effects of pyrogens on an inexperienced immune system.

“Feed a cold, starve a fever.” Should a feverish person eat little or nothing, as the saying suggests? Yes. During fever, all the body's functions are occurring amid increased physiological stress. Provoking digestion during such physiological stress overstimulates the parasympathetic nervous system when the sympathetic nervous system is already active. As a result, it is possible that during a fever the body could misinterpret some substances absorbed from the gut as allergens. Finally, excessive fever can, on rare occasions, trigger seizures, collapse and delirium—all of which may be further complicated by recent eating.

Sometimes fever can climb too high for the body's own good. Temperatures exceeding 105 degrees F, for instance, can threaten the integrity and function of vital proteins. Cellular stress, infarction (heart attack), tissue necrosis, seizures and delirium are among the potential consequences. If a fever outpaces the body's own temperature-reduction mechanisms, “cooling blankets” or other methods can help.

Why do we put salt on icy surfaces in the winter?


The late John Margrave, a chemistry professor at Rice University, provided this answer:

In short: salt makes the ice melt.

All ice-covered areas in fact have small puddles of water. Applied to such surfaces, the salt dissolves. Liquid water has what is known as a high dielectric constant, which allows the salt's ions (positively charged sodium and negatively charged chlorine) to separate. These ions, in turn, hydrate—that is, they join to water molecules. This process gives off heat, which in turn melts microscopic parts of the ice surface. Thus, a substantial amount of salt spread over a large surface can thaw the ice. And as automobiles roll along, the pressure helps to force the salt into the ice, and so more hydration occurs.

Much of the rock salt applied in the winter is the same substance that comes out of your saltshaker. The only difference is that rock salt has crystallized in larger pieces, whereas table salt is ground to a more or less uniform size. Calcium chloride, manufactured from brines and other natural materials, is just as commonly used to melt ice on the streets as sodium chloride is.

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