Letters.

Burning questions

Why am I not surprised that the pH of lung moisture decreases during an asthma attack ("Antacids for asthma sufferers?" SN: 4/8/00, p. 239)? Poor ventilation of the alveoli would retain carbon dioxide, which is carbonic acid in solution. Does the change in pH correspond to a buildup of carbonate or bicarbonate in the blood? Would it be a better measure of an asthmatic episode to measure [CO.sub.2] retention?

Bart Bresnik Mansfield, Mass.

I wonder if the acidity of the exhaled moisture was due to acidity in the lung fluid or to refluxed fluids from the upper gastrointestinal tract. Very often, chronic cough and asthmalike symptoms are due to gastroesophageal reflux disease (GERD), and not due to asthma. This could have implications for treatment, as antacids would not be of use if the acidity were in fact due to acidic pulmonary fluid. This is obviously preliminary work, and as is usual with good science, it raises more questions as it searches for answers.

Gregory F. Nye North Falmouth, Mass.

Researcher Benjamin Gaston of the University of Virginia Health System in Charlottesville replied to the first letter, "Carbon dioxide levels tend to be slightly low, if anything, in patients with asthma. We actually controlled very carefully for [CO.sub.2], fastidiously removing it from each sample.... What we saw had little or nothing to do with blood pH/[CO.sub.2]." To the second letter, Gaston answers that none of the patients had GERD symptoms and that several aspects of the study rule out GERD. "We believe that we have now defined the biochemical basis for low airway pH in these patients, and it doesn't involve GERD or stomach acidification mechanisms," says Gaston.

--D. Christensen

Life's little setbacks

"The meaning of life" (SN: 4/29/00, p. 284) seems to contain a few errors. Codons are found on the messenger RNA. Therefore, they can't contain thymine. They must have uracil, instead. The RNA codon AUG (your ATG) is the only codon for methionine. If it is the "start" codon, how is methionine coded?

Nicholas L. Reuter University of Cincinnati Cincinnati, Ohio

Most geneticists and genetics textbooks refer to both DNA and RNA triplets as codons. The AUG mRNA codon codes for methionine and also acts as the start codon for all proteins. However, we did make mistakes in the article "Code breakers" (SN. 6/3/00, p. 360) on a related topic. In the table in that article, the abbreviation for the newly introduced glutamine should be Gln not Glu. The figure wrongly gives Asn as the abbreviation for glutamine.

--The editors

Fine feathered friends?

Reading "Do oxpeckers help or mostly just freeload?" (SN: 4/29/00, p. 278), I was struck with a question: Do the oxen form a psychological attachment to their oxpeckers (and vice versa)? One way of finding this out would be to observe whether the oxpeckers remain attached to one ox or are fickle partners.

Jeff Leer Fairbanks, Alaska