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Thermal Musings

Philip Morrison

Body Heat: Temperature and Life on Earth. Mark S. Blumberg. x + 240 pp. Harvard University Press, 2002. $22.

A Matter of Degrees: What Temperature Reveals about the Past and Future of Our Species, Planet, and Universe. Gino Segrè. xx + 300 pp. Viking, 2002. $24.95.

Body Heat and A Matter of Degrees both center on the subtle concept of temperature. In the former, neurobiologist Mark S. Blumberg opens with a reminder that our existence depends on our planet being the right distance from the Sun (we forget, he says, that "Pluto is cold; Chicago in January is merely inconvenient") and then moves quickly to a close examination of body heat in the many forms of life that have arisen in "the narrow thermal window of organic opportunity" that Earth presents. In the latter book, Gino Segrè, a theoretical physicist, begins with a consideration of body temperature and eventually extends his journey to the cosmos, absolute zero and the quantum. These two physics books, which make little use of symbols, should charm attentive readers from all walks of life.

Blumberg tells us that nearly all mammals regulate their body temperature at 97 to 100 degrees Fahrenheit (marsupials are a little cooler, at 95 to 97 degrees, and egg-laying mammals like the platypus are a lot cooler—86 to 88 degrees). Ostriches are warmer (102 to 104), and songbirds warmer still (104 to 106). It is no surprise that complex biochemical systems with an internal energy source evolve to remain near some optimum temperature. Death comes more often with body temperatures that are too high; in humans, excursions above 108 degrees are deadly. Cold can inactivate reactions, but it takes mechanical injury at the cellular level from the formation of ice crystals to destroy the macromolecules we live by.

A neutrino detector in SudburyClick to Enlarge Image

Is fever good or bad—a genuine defense against infection, or merely damage to vulnerable controls? Experiments as picturesque as they are compelling were carried out in the 1970s by the American physiologist Matthew Kluger, using desert iguanas kept in a big indoor pen. Such "cold-blooded" reptiles cannot change their internal heating; their body temperatures depend on the ambient conditions, sunlight especially. Kluger arranged close temperature monitoring for a dozen or so healthy lizards, placing them for 24 hours in an environment in which they were free to move among locations of different temperatures. Yet the body temperature of each averaged 100 degrees. (Thermoregulation by judicious moving appears to serve reptiles well.) The iguanas were then infected with a dose of dead bacteria that induced a fever but could not cause lasting illness. Within hours they had all found warmer spots; by the next day, they were averaging body temperatures of 108 degrees. Next he infected them with live bacteria and kept each in a fixed location at one temperature—some at 108 degrees and others at temperatures from 93 to 104. Three days after being infected, nearly all of the lizards kept at 108 degrees were still alive, nearly all held at 93 had died, and those kept at intermediate temperatures had intermediate survival rates. No conflicting data have been found, although similarly challenged mammals (rabbits) survive best when the fever they develop remains moderate. Fever is pretty surely a beneficial response of the organism, as its complex biochemical features have always signaled.

Body Heat includes much more than we can mention. One complex issue Blumberg discusses is obesity. Normally, overeating leads to an increased rate of heat production; some people sweat after a heavy meal. This diet-induced thermogenesis is no mere by-product of hard digestive work; it comes from brown adipose tissue, which produces heat to burn off excess fat. The hormone leptin promotes this reaction, but obese people appear to be insensitive to leptin.

Blumberg's own research includes studies of the sleep intervals characterized by vivid dreaming and rapid eye motion (REM sleep). During these intervals, intense activity occurs in many parts of the body and brain, but thermoregulatory responses to heat and cold are inhibited: During other sleep intervals, we may shiver or sweat, but during REM sleep we cannot, Blumberg tells us, and our body temperature rises or falls with the prevailing environment. This thermal vulnerability is limited, though; we can only fall into REM sleep within a set range of temperatures.

Segrè introduces A Matter of Degrees with an engaging personal account of how he came by his interest in thermometry, confiding that physics is his "family business"—a Nobelist uncle, a brother, wife, in-laws and "plenty of cousins" are in the same trade.

The opening chapter on body temperature is followed by one on history, which discusses topics such as firemaking, smelting, steam power and the laws of thermodynamics, as well as the four inventors of the thermometer. The latter included Galileo and his friend Santorio—a professor of theoretical medicine at Padua who put a scale on a thermoscope (a device that showed the change in a gas as it was heated or cooled) and became the first person to measure body temperature systematically. Chapter three deals with climate change and chapter four with life at the extremes—hydrothermal vents, the origin of life and extraterrestrial life. Chapters five and six include discussions of cosmology and quantum mechanics.

Segrè holds "a sentimental fondness for how heat emanates from the Sun." He recalls with affection George Gamow and his lighthearted book The Birth and Death of the Sun (1940)—which Segrè tells us was "the first real science book I ever read." In 1938 Gamow invited Hans Bethe to a meeting on nuclear reactions in stars. Bethe, "totally uninterested in astrophysics" at that time, declined. Happily, he was eventually persuaded to come and became fascinated with the subject. Within six months, he had worked out the specific nuclear reactions that have allowed our sun to shine so hotly for so long.

Neutrinos, free particles that are elusive in their indifference to most familiar interactions, bring us data direct from the solar core. We have reason to believe neutrinos generated early in the history of the universe still abound—that several thousand neutrinos fill every cubic inch of space and are in thermal equilibrium at 2 kelvins—just as photons of the cosmic microwave background are in thermal equilibrium at about 3 kelvins. Although these neutrinos have not been detected, Segrè muses on how one day they might be studied.

Segrè ends his book with a fresh account of the great quantum leap, showing how quantum mechanics makes comprehensible the behavior of atoms at temperatures near absolute zero. He begins with Max Planck's daring theory postulating that energy is emitted and absorbed not continuously, but in steps, or fixed packages, called quanta. In this chapter Segrè, rather than trying to make plausible the paradoxes of the quantum world (such as wave-particle duality), summarizes how much the quantum has allowed us to understand, including phenomena such as Bose-Einstein condensation. The latter occurs when whole populations of identical vapor atoms crowd into one single quantum state, losing many familiar properties of individuality, at temperatures only 200 billionths of a degree above absolute zero.

These two very agreeable, instructive and yet quite distinct books on temperature form a happy duality in themselves.-Philip Morrison, Institute Professor Emeritus, Massachusetts Institute of Technology, and Phylis Morrison, Cambridge, Massachusetts


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