Summary
By developing a clever technique for studying a hamster's retina in culture, investigators have found that it hosts a biological clock, secreting varying amounts of the hormone melatonin over a 24-hour cycle. The finding, reported on page 419, brings to two the number of biological clocks known in mammals—the other is in a brain structure called the suprachiasmatic nucleus—and brings mammals into line with other vertebrates, which have multiple clocks. It will also provide investigators trying to tease apart the workings of these clocks with a valuable experimental model.
