Anyone who has not had the pleasure of getting to know a rat personally could be forgiven for thinking that the aggressive disease-spreading reputation of wild rats bore some relation to how pet rats behave. In fact nothing could be further from the truth.

Pet rats are gentle, intelligent creatures who learn quickly and make charming and really interesting pets. They are more likely to catch illnesses from us than us from them.

Milo is a fawn and white female rat of about two years old, who I saw recently. Her owner had noticed a lump just behind her right foreleg, low down over her ribs about the size of a 20p piece.

They had noticed it about a week previously and since then it had grown a little. When I examined Milo I found that the lump moved freely with the skin. She seemed uncomfortable when I touched the lump although she had not lost weight and did not show any other signs of illness.

I explained that the lump was probably a growth although it might turn out to be an abscess. It was most likely to turn out to be a mammary tumour, a growth in the milk-producing tissue of which both rats and mice have a great deal in order to feed their large families.

The chances of successfully curing the lump without cutting it out were poor whatever it was.

There is an important difference between rats and mice when it comes to mammary tumours. Both rats and mice quite often get them, but while they are often malignant in mice they are usually benign and therefore easier and more rewarding to treat in rats as they rarely spread to other parts of the body or grow back again.

The fact that rats are larger than mice makes it a little easier and safer to operate on them. Rats' stomachs are quite slow to empty after eating so I arranged for Milo to be starved from 10pm on the day before her operation. The next morning I took her to the operating theatre.

She sat still and quiet as I put her into a rubber mask and gave her the gas to make her go to sleep. Ten minutes later, her operation done, she was back in the incubator keeping warm as she woke up. By the afternoon she was pottering about her cage very much as if nothing had happened.

The lump was indeed a mammary tumour so now it is fingers crossed that it does not come back.

Converted for the new archive on 30 June 2000. Some images and formatting may have been lost in the conversion.