SCIENCE

Fetuses do not breathe air but inhale and exhale amniotic fluid. Prematurely born babies as young as 25 weeks of gestation can cry immediately after birth, indicating that the physical capacity is present.

Mitchell said he is not sure what the finding says about a 28-week fetus's capacity to consciously interpret pain -- an issue that has recently gained attention in light of efforts to require that anesthesia be given to fetuses about to be aborted. It is widely accepted that the brain connections needed to experience pain are fully wired by 30 weeks of gestation, and perhaps by 25 weeks or earlier, Mitchell said.

If fetuses do cry, he added, the cries are silent -- there is no air to flow past the developing vocal cords.

-- Rick Weiss

Nuclear Tests Help Estimate Age

"CSI" fans, take note. Estimates of a body's age at the time of death may soon be much more accurate, thanks to an odd legacy of aboveground nuclear bomb tests of the 1950s and '60s.

The Cold War testing produced fallout that sharply increased levels of radioactive carbon-14 in the atmosphere, but since the Test Ban Treaty of 1963 (and for a long time to come), those concentrations have been dropping at a known rate.

Like other forms of carbon, the isotope reacts with oxygen to form carbon dioxide, which gets taken up by plants via photosynthesis.

People who eat vegetables end up with the same concentration of carbon-14 in their bodies as in the plants and the air. But because tooth enamel forms only once, it becomes a permanent record of the concentration at the time, and that can be measured. And because teeth develop at predictable ages until about age 12, knowing what year a tooth formed provides a good estimate of a person's age.

Researcher Jonas Frisen of Stockholm's Karolinska Institute, with colleagues in Sweden and California, tested the method on 22 people, and they were able to gauge their ages to within about 1.6 years. That's more accurate than current methods based on bone development and tooth wear.

Only one problem: People born before 1943 had formed all their teeth before the testing began. For them, all that this method can determine is that, as of now, they are at least 62. But that, the researchers wrote in the Sept. 15 issue of the journal Nature, they know "with a high degree of certainty (100 percent . . .)."

-- Nils Bruzelius