Heliophage


Review: The Atlantic
June 12, 2009, 10:23 am
Filed under: Reviews received

Another very nice capsule review in one of my favourite magazines

This original account of photosynthesis does what every popular-science work strives to do: provide a lucid-to-the-lay-reader explanation of a mundane or complex phenomenon. Yet Morton goes well beyond that laudable achievement. Folded cunningly into his disciplinary synthesis (physics, chemistry, cellular biology, environmental science) and basic explainer (what, exactly, photosynthesis is, and why apprehending “the most important process on the planet” is crucial to our understanding of today’s pressing energy and climate-change issues) is nothing less than a majestic terrestrial biography—a meticulous look at the history and future of the Earth itself. All this is in a well-paced, smartly plotted, bouncingly written package. Buoyed by a tone of optimism and uplift (“The science that enriches our wonder at the world also offers us ways of making things better”), Morton’s clear-eyed assessment makes visible a heretofore unseen world—ours—and illuminates its possibilities.

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2 Comments so far
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I am enjoying Eating the Sun. Re: Mayer’s thought (p.52) that venous blood in feverous patients in the tropics contains more oxygen because the ambient temperature is higher so body uses less oxygen. This is unlikely to be an effect significant enough to be visible to the naked eye. Mayer had only been a physician for two years at that point, i.e. inexperienced. Venous blood of patients with sepsis is oxygen-rich regardless of ambient temperature: 1)bacterial proteins inhibit host cellular uptake/use of oxygen; 2)cutaneous vasodilatation accompanying fever shunts oxygen-rich arterial blood directly to veins. Cause 2) may occur with high ambient temperature alone. Conversely, cutaneous vasoconstriction in cold environments tends to decrease oxygen in venous blood because sluggish bloodflow and extra capillary transit time allow greater oxygen uptake by cells – not because of a decrease in cellular metabolic rate. Cause 1) is presumably an evolved bacterial mechanism that limits host’s defensive capabilities. In sum, the phenomenon Mayer noted is not due to the cause he postulated.

Comment by dwight bramble md

Addendum: Severe natural hypothermia, e.g. causing coma, does decrease cellular metabolic rate. But it also decreases oxygen uptake and delivery commensurately: these patients have very slow breathing and heart rates (even zero in the case of cold-water drowning victims who have been successfully resuscitated after prolonged emersion). The oxygen level in their venous blood is affected not just by oxygen delivery and metabolic rate, but also by changes in hemoglobin function and blood/oxygen solubility during hypothermia, making causality difficult to pinpoint. The hypometabolic state of medically induced hypothermia is of course a whole different kettle of fish, i.e. oxygen delivery is controlled.
Decreased venous oxygen levels during mild natural hypothermia, e.g. person is still conscious, are due to the causes stated in the first note.

Comment by dwight bramble md




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