"Why," asked an elementary school student named Adam, "is there no mammal with green fur? Green is a good camouflage color, and nonmammals (for example, frogs, snakes and birds) do come in green. Why no mammals?"

It wasn't the kind of question Alexey Veraksa, an assistant professor of biology, usually handles in his laboratory at the University of Massachusetts. But Veraksa jumped at the chance to answer -- with relish. He produced a well-researched 13-paragraph response.

The question came to Veraksa through "Ask a Scientist," a Web site operated by the Howard Hughes Medical Institute that allows anyone to ask a scientific question and get an answer from a working scientist, said Katherine Wood, who coordinates the project.

About 3,500 questions are sent in every year, and every serious query gets a response from one of nearly 50 institute scientists. Questions that are "outside the box," Wood said, are posted on the Web site:

* What is the molecular mechanism for stripes in zebras?

* How are memories retained?

* Does exposure to cold weather make a person catch a cold or the flu? If yes, how does it happen? If no, why do people say that we get ill more easily in cold weather? And why does the flu season occur during the winter?"

And there are more esoteric questions that have a more limited audience: "Can macrophages from one person activate lymphocytes from another?"

Questions that won't get answered, said Web site editorial manager Dean Trackman, are homework questions, which are obvious because some students send in textbook multiple-choice questions.

Other science Web sites answer questions from readers, but many focus on a particular subject or don't answer every question.

About 65 percent of the questions sent to Ask a Scientist come from the United States, most from high school students. But some of the most interesting questions, Wood said, come from the really young.

"They ask such incredibly basic questions that we don't think about often," Wood said. "For example, one asked, 'Is the iron in our food metal?' "

Well, is it?

"Someone is working on that!" she said.

* For the answer to these and other questions, go to "Ask a Scientist" at: askascientist.org or www.hhmi.org.