LONDON — Dutch and Norwegian scientists say they have solved a glowing mystery: why Rudolph the reindeer’s nose is red.

By traveling to the Arctic and using video-microscope and thermal imaging technology, the scientists showed that the glow is from tiny blood vessels that are more abundant in the noses of reindeer than in humans’. Yes, seriously. The findings are being reported next week in BMJ, formerly known as The British Medical Journal, a publication with a quirky holiday tradition.

For the past 30 years, BMJ has devoted its Christmas-week issue to a lighter and sometimes brighter side of medicine, publishing unusual articles that vary from simply amusing to bizarre to creative or potentially important. All are based on methodologically sound science.

Alongside Rudolph on the cover of this year’s holiday issue is Cliff, a 2-year-old beagle who was trained by another Dutch team to accurately sniff out the sometimes fatal bacterial bowel infection Clostridium difficile and make the diagnosis in minutes — days faster than standard laboratory tests. The Christmas tradition began in 1982, originally intended as a one-time effort to give readers a break from stodgy scientific reports written in technical jargon. The editor then, Dr. Stephen P. Lock, recalled in an interview that he wanted to present “another side of medicine” by offering lighter reading: research oddities, bizarre stories and history. But this was no April fools’ issue: Dr. Lock insisted that the articles meet the same rigorous criteria as research published in regular issues.