Web edition: April 5, 2005
Print edition: April 9, 2005; Vol.167 #15 (p. 239)

Big ideas

Your article "Life on the Scales" (SN: 2/12/05, p. 106) reminded me that taking a bird's song and transposing it down four octaves makes it sound like a whale's song. The opposite is also true. To hear this, go to http://www.mind.net/music/birdwhaleDemo.mp3.

Todd Barton
Ashland, Ore.

The article would imply that the only anomaly to the theory that mass equates to longevity is that large-dog breeds live shorter lives than small ones do. I would suggest that there are many more discrepancies. For example, humans outlive elephants, horses, and cows, and tortoises outliving humans. And amoebas outlive us all.

McClellan Blair
Indiana, Pa.

This is tremendously interesting. The scaling law is evidently expressible in a single formula. Why not present it?

Patrick J. Roache
Socorro, N.M.

Here's the equation, I = i₀ M^3/4e^–E/kT. I is an individual's metabolic rate, i₀ is a normalization constant, M is mass, E is the activation energy, k is Boltzmann's constant, and T is body temperature in kelvins.—E. Klarreich

No bargain

"High costs of CT screening" (SN: 2/19/05, p. 125) overlooks an immeasurable long-term cost of whole-body computed tomography scans: the potential cancers induced by high-dose radiation. Aggressive marketing of CT scans without full disclosure of the risk is unethical and should be illegal.

Nancy Evans
San Francisco, Calif.

Pressure point

"Against the Migraine" (SN: 2/19/05, p. 119) mentions several possible triggers for migraines, with a patent foramen ovale being one. There is also the change-in-weather trigger, from which I suffer. All the symptoms mentioned in the article could cause a fairly sudden change in blood pressure. A weather-related change in barometric pressure might have the same effect. I wonder if there's a common mechanism in how migraine victims' bodies handle changes in pressure.

Dotti Lydecker
Lake San Marcos, Calif.