The healing power of pets has gone from something akin to an old wives' tale to being embraced by health boards, hospices and secure units.

It is known that the mere action of stroking a dog or cat slows down the heartbeat and reduces blood pressure as well as inducing feelings of wellbeing.

I'm about to witness first-hand the effect an animal has on patients as I arrive at the Prince and Princess of Wales hospice in Glasgow with Mac, my bearded collie, who is volunteering as a therapy dog for the afternoon.

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Having had only a short walk today and a relatively long car journey, he is worryingly full of bounce. An aura of calm is a pre-requisite for a therapy dog. Sure enough, as we step into the reception it's a case of sensory overload. Phones are ringing, new smells fill the air, people are walking past. A few visitors wave to Mac and he's immediately up on his hind legs, tail going like a helicopter blade as he strains to run across the room and plant a slobbery kiss on someone's face. I lose my nerve and duck back outside to let him – and me – cool off. After 10 minutes round the block we try again.

By this time James MacDonald of Therapet, a service run by the charity Canine Concern Scotland Trust, has arrived. James came to our home earlier in the week to assess Mac's suitability and is confident he can handle it. Dogs – and cats – must be friendly and outgoing without being too boisterous. The animals who fail are likely to need more socialisation. All volunteers are vetted.

After 10 minutes adjusting to his new surroundings, Mac enters the main lounge, where he is greeted with a ripple of excitement. All pink tongue and fluffy beard, he pulls towards the welcoming hands as they move in for a pat.

Stan Wood, 57, and Tam Lyons, 63, are in the middle of a game of dominoes but play is suspended to greet Mac and conversation turns to the dogs they have owned. Both men are in electric wheelchairs, which can sometimes confuse animals, but Mac isn't fazed. I've been instructed to keep him on a short lead and with all four paws on the floor, but the men encourage him to jump up for a proper hug and he obliges.

A circle forms around him as staff drop in to meet him and passing patients stop to chat. "What's his name?" "What kind of dog is he?" "How old is he?"

James, a retired fireman who has volunteered for more than 20 years with his old English sheepdogs, had prepared me for such a reaction. "It's not just patients who enjoy seeing the dogs. It creates a talking point between visitors and patients and can be a real stress reliever for staff."

Josie Livingston, 82, who is doing crafts at the table, reveals that she bred dogs for 20 years. Another woman brings out a photograph of her much-loved dog, which passed away. While conversations start with dogs, they spiral off in all directions. While the dog is in the room, thoughts are far from illness.

After 90 minutes of socialising, Mac is wiped out. He slides to the floor and closes his eyes. As he bids a fond farewell, he leaves behind not only a trail of Bonio crumbs but a raft of happy faces. I can honestly say I have never been more proud of him.

Read Mac and Me - the dog blog here.