CLOCKS AND RHYTHMS

CLOCKS AND RHYTHMS
Alvin Silverstein, Virginia Silverstein,
Laura Silverstein Nunn
Brookfield CT: Twenty-First Century Books, 1999
64 pages, hardback, $23.40
ISBN 0-7613-3224-3

Reviewed by Lynne Lamberg

This is a nice introduction to biological rhythms, simple but not simplistic. Though children aged 9 to 12 are the book's primary audience, high school students and adults may find it informative, too. It begins by noting that internal clocks "tell you when to feel hungry, sleepy, or wide awake," noting that some animals are active in the daytime and others at night.

The authors describe daily, monthly, and annual rhythms, addressing the sun's rotation on its axis and the changing of seasons. Color illustrations with clear captions amplify the text. They show the impact of tidal changes, for example, with photos taken at the same location at high tide and low tide.

Sundials, waterclocks, and Aztec calendars introduce readers to the concept of measuring external time. From there, the authors move to internal time, reviewing early studies in which botanists manipulated plants' daily leaf opening and closing, and bees' daily arrival at feeding tables. They describe sleep and time isolation studies, including Nathaniel Kleitman's two months in Mammoth Cave, Kentucky, in 1938, and more recent work in sleep laboratories.

They discuss the implications of biological rhythms for the treatment of diseases, including winter depression, also called Seasonal Affective Disorder, or SAD. They tell how disruptions in body clocks cause trouble sleeping and difficulty concentrating in jet travelers and shift workers, and describe industrial catastrophes related to shift worker performance, such as that at Three Mile Island.

The text notes that body time is controlled by the suprachiasmatic nucleus or SCN, a cluster of cells within the hypothalamus, and describes the pathways that light follows from the retina. The scientific terms are clearly defined, and the book includes an excellent glossary. It also includes books for further reading and a list of Internet resources, not, unfortunately, including http://www.sleephomepages.org, where interested readers can use BiblioSleep to find more information on the book's topics.