which diminish the immune attack and the resulting
inflammation.
Toxicodendron Dermatitis
When people get urushiol—the oil present in poison
ivy, poison oak, and poison sumac—on their skin, it
causes another form of allergic contact dermatitis (see
above). This is a T-cell-mediated immune response, also
called delayed hypersensitivity, in which the body’s
immune system recognizes as foreign and attacks the
complex of urushiol derivatives with skin proteins. The
irony is that urushiol, in the absence of the immune
attack, would be harmless.
Atopic Dermatitis
Atopic dermatitis is a chronic, itchy inflammation of
the upper layers of the skin. Often develops in people
who have hay fever or asthma or who have family
members with these conditions. Most commonly dis-
played during infanthood, usually disappearing by the
age of three or four. Recent medical studies suggest that
Staphylococcus aureus(a bacteria) contributes to exac-
erbation of atopic dermatitis.
Treatment is similar to that of contact dermatitis.
Seborrheic Dermatitis
An inflammation of the upper layers of the skin where
scales appear on the scalp, face, and sometimes in other
areas. Usually more common in cold weather and often
runs in families.
Stasis Dermatitis
Achronic redness, scaling, warmth, and swelling on
the lower legs. Often results in dark brown skin due to
a pooling of blood and fluid under the skin, thus usual-
ly displayed by those with varicose veins and edema.
rate-controlling step (rate-determining step; rate-
limiting step) A rate-controlling step in a reaction
occurring by a composite mechanism is an elementary
reaction, the rate constant for which exerts a dominant
effect—stronger than that of any other rate constant—
on the overall rate.
Réaumur, René-Antoine Ferchault de(1683–1757)
FrenchPhilosopher, Naturalist René Réaumur was
born in La Rochelle, France, in 1683. After studying
mathematics in Bourges he moved to Paris in 1703 at
age 20 and under the eye of a relative. Like most scien-
tists of the time, he made contributions in a number of
areas, including meteorology. His work in mathematics
allowed him entrance to the Academy of Sciences in- Two years later, he was put in charge of compil-
ing a description of the industrial and natural resources
in France, and as a result he developed a broad-based
view of the sciences. It also inspired him to invention,
which led him into the annals of weather and climate
and, ultimately, the invention of a thermometer and
temperature scale.
In 1713 Réaumur made spun-glass fibers that were
made of the same material as today’s building blocks of
Ethernet networking and fiber-optic cable. A few years
later, in 1719, after observing wasps building nests, he
suggested that paper could be made from wood in
response to a critical shortage of papermaking materials
(rags) at the time. He also was impressed by the geomet-
rical perfection of the beehive’s hexagonal cells and pro-
posed that they be used as a unit of measurement.
He turned his interests from industrial resources
such as steel to temperature, and in 1730 he presented to
the Paris Academy his study “A Guide for the Produc-
tion of Thermometers with Comparable Scales.” He
wanted to improve the reliability of thermometers based
onthe work of Guillaume Amontons, though he appears
not to be familiar with Fahrenheit’s earlier work.
His thermometer of 1731 used a mixture of alco-
hol (wine) and water instead of mercury, perhaps creat-
ing the first alcohol thermometer, and it was calibrated
with a scale he created called the Réaumur scale. This
scale had 0° for freezing and 80° for boiling points of
water. The scale is no longer used today. However,
most of Europe, with the exception of the British Isles
and Scandinavia, adopted his thermometer and scale.
Unfortunately, his errors in the way he fixed his
points were criticized by many in the scientific communi-
ty at the time, and even with modifications in the scale,
instrument makers favored making mercury-based ther-
mometers. Réaumur’s scale, however, lasted over a cen-
tury, and in some places well into the late 20th century.
Between 1734 and 1742, Réaumur wrote six vol-
umes of Mémoires pour servir à l’histoire des insectes
(Memoirs serving as a natural history of insects).
Although unfinished, this work was an important con-
tribution to entomology. He also noticed that crayfish
286 rate-controlling step