A happy tail wag makes just about everybody smile. Accompanied by their owners, therapy dogs visit hospitals and nursing homes, spreading special medicine to help patients recover from everything from depression to cancer surgery.

These canine volunteers lift spirits, encourage interaction and reduce stress. The dogs love it too, and tails really get going when it’s visit time.

But these uncanny canines also need to be prepared. They have to learn specific behaviors, such as ignoring dangerous objects and treading gingerly around walkers and wheelchairs. A calm outgoing personality is a must.

Anecdotal reports suggest that therapy visits elevate patients’ moods and lower blood pressure and stress. Canine intuition also plays a part, with dogs instinctively seeming to know what each patient needs. Maybe M.D. should also stand for mutt doctor?