technique. Good for dates between 10,000 and
230,000 years.
radionuclide A radioactive nuclide. The term
nuclideimplies an atom of specified atomic number
and mass number. In the study of biochemical process-
es, radioactive isotopes are used for labeling com-
pounds that subsequently are used to investigate
various aspects of the reactivity or METABOLISMof pro-
teins, carbohydrates, and lipids or as sources of radia-
tion in IMAGING. The fate of the radionuclide in
reactive products or metabolites is determined by fol-
lowing (counting) the emitted radiation. Prominent
among the radionuclides used in biochemical research
are :^3 H,^14 C,^32 P,^35 Ca, 99mT c,^125 I, and^131 I.
ragweed(Ambrosia) Ragweed refers to the group of
approximately 15 species of weed plants, belonging to
the Compositae family. Most ragweed species are
native to North America, although they are also found
in eastern Europe and the French Rhône valley. The
ragweeds are annuals characterized by their rough,
hairy stems and mostly lobed or divided leaves. The
ragweed flowers are greenish and inconspicuously con-
cealed in small heads on the leaves.
The ragweed species, whose copious pollen is the
main cause of seasonal allergic rhinitis (hayfever) in
eastern and middle North America, are the common
ragweed (A. artemisiifolia) and the great, or giant, rag-
weed (A. trifida). The common ragweed grows to
about 1 meter (3.5 feet), is common all across North
America, and is also commonly referred to as Roman
wormwood, hogweed, hogbrake, or bitterweed. The
giant ragweed, meanwhile, can reach anywhere up to 5
meters (17 feet) in height and is native from Quebec to
British Columbia in Canada and southward to Florida,
Arkansas, and California in the United States. Due to
the fact that ragweeds are annuals, they can be eradi-
cated simply by being mowed before they release their
pollen in late summer.
rain forest An evergreen forest of the tropics distin-
guished by a continuous, closed canopy of leafy trees of
variable height and diverse flora and fauna, with an
average rainfall of about 100 inches per year. Rain
forests play an important role in the global environ-
ment, and destruction of tropical rain forests reduces
the amount of carbon dioxide absorbed, causing
increases in levels of carbon dioxide and other atmo-
spheric gases. Cutting and burning of tropical forests
contributes about 20 percent of the carbon dioxide
added to the atmosphere each year. Rain forest destruc-
tion also means the loss of a wide spectrum of flora
and fauna.rash(dermatitis) An inflammation of the upper lay-
ers of the skin, causing rash, blisters, scabbing, redness,
and swelling. There are many different types of der-
matitis, including: acrodermatitis, allergic contact der-
matitis, atopic dermatitis, contact dermatitis, diaper
rash (diaper dermatitis), exfoliative dermatitis, herpeti-
formis dermatitis, irritant dermatitis, occupational der-
matitis, perioral dermatitis, photoallergic dermatitis,
phototoxic dermatitis, seborrheic dermatitis, and toxi-
codendron dermatitis.Contact Dermatitis (allergic contact dermatitis, con-
tact eczema, irritant contact dermatitis)
Contact dermatitis is a reaction that occurs when skin
comes in contact with certain substances. There are
two mechanisms by which substances can cause skin
inflammation: irritation (irritant contact dermatitis) or
allergic reaction (allergic contact dermatitis). Common
irritants include soap, detergents, acids, alkalis, and
organic solvents (as are present in nail polish remover).
Contact dermatitis is most often seen around the hands
or areas that touched or were exposed to the
irritant/allergen. Contact dermatitis of the feet also
exists, but it differs in that it is due to the warm, moist
conditions in the shoes and socks.
An allergic reaction does not generally occur the
first time one is exposed to a particular substance, but
it can on subsequent exposures, which can cause der-
matitis in 4 to 24 hours.
Treatment includes removal or avoidance of the
substance causing the irritation, and cleansing the
area with water and mild soap (to avoid infection). A
recent recommendation for mild cases is to use a man-
ganese sulfate solution to reduce the itching. Antihis-
tamines are generally not very helpful. The most
common treatment for severe contact dermatitis is
with corticosteroid tablets, ointments, or creams,rash 285