IT STARTED out as a plot device. Novelist as God How to keep Irene, a central character in the novel I was writing, out of circulation for her early adult years. I thought of sending her to prison, or giving her a vocation and packing her off to a convent.

The third option was illness. And since the novel is set in the 1950s in Ireland, the obvious choice was tuberculosis, a subject about which I knew next to nothing.

Before the introduction of the drugs Streptomycin and Isoniazid in the early 1950s, the diagnosis of TB was equivalent to a death sentence. It is difficult to imagine now the horror with which the disease was greeted, except perhaps to compare it with AIDS.

Like AIDS it is an infectious disease and carried with it all the same mistaken associations of punishment, guilt and shame, and, of course, the dread of contagion.

And it swept through the country taking young and old alike. Almost 10,000 people died from TB between 1950 and 1960. But for what was a virtual epidemic, much of what survives of it is anecdotal. Perhaps, like the Great Famine, it will take us 150 years to come to terms with the social catastrophe that was TB. Yet for those of my parents generation born in the 1920s there are few who would not have been touched by the illness.

I remember my mother talking of a young neighbour in rural Kerry, a 12 year old boy, who died from TB. She remembers visiting him as he lay dying at home. His shroud was already laid at his feet. In those days, TB was not something you recovered from.

A friend of mine whose mother contracted TB when he was a baby recalls her stories from the sanatorium, mostly of the appalling frequency of death. She was one of the lucky ones. Left out on a corridor to die, she was spotted by Dr Noel Browne who refused to give her up as a lost cause.

The figure of Noel Browne stands proud and majestic over the history of TB in this country. He had good reason to be familiar with tuberculosis his mother and two of his sisters died from the disease and he himself fell victim to it in his early 20s.

As a young doctor he worked in several sanatoriums and observed what he described in his autobiography as "the old, rigid arrogant class attitudes" in the medical establishment where doctors insisted on being called "Sir" while the hospital roof leaked into buckets on the ward floors and there were hundreds of patients on the waiting list.

As Minister for Health, he instituted a wide ranging tuberculosis programme including a mass radiography scheme which by July, 1950, had increased the number of TB beds to 5,500 and had reduced the death rate to 73 per 100,000 by 1951.

BUT this was all knowledge I had yet to come by. Meanwhile, I had a character stranded in a sanatorium on my hands. I was living in Italy at the time which made the task harder. There in the midst of a glorious Umbrian spring, the fields blazing with wild poppies and the sun filtering through the cypresses, I had to transport myself and her back to the dank world of a 1950s institution.

I had never, to my knowledge been in a sanatorium. (In fact I discovered that this was not the case. Several hospitals in the Dublin vicinity such as Peamount, Cherry Orchard, the Royal Hospital in Donnybrook, had been used as sanatoriums even the Pigeon House had once been a sanatorium.) The only reference book I had to hand was Noel Browne's autobiography, Against the Tide, which gave me an overview of the epidemic but not what it was like to be a patient in a sanatorium.

There was another source of information, of course. The work of other writers. Keats, Shelley and Kafka all suffered from TB and wrote about it. There was Thomas Mann's classic, The Magic Mountain, set in a Swiss sanatorium. But these literary renditions of TB seemed a long way from what I was trying to describe.

The romantic poets saw TB or consumption in idealised, mythic terms. Shelley wrote to Keats comforting him with the assertion that the disease was "particularly fond of people who write such good verses as you have done..." Byron longed to suffer from it because the ladies would say "how interesting he looks in dying". Hence, pale and interesting.

SUSAN Sontag in her book, Illness as Metaphor, notes how this literary romanticisation of TB lent credence to the notion that it was a disease of passion, afflicting the reckless and sensual. "For over a hundred years TB remained the preferred way of giving death a meaning an edifying, refined disease. Nineteenth century literature is stocked with descriptions of almost symptom less, unfrightened, beatific deaths from TB," Sontag writes.

The reality was a lot grimmer. Here is how actor John Molloy described his course of treatment in Newcastle Sanatorium in his autobiography, Alive Alive O. "They pumped air into the chest wall to depress your lung. I was on two twice a week, a thing like a knitting needle, banged into your stomach and then one in your side no anaesthetic for after tour years of refills of one kind or another you got used to them, well, not really, but you told yourself you did."

And death, when it arrived, was no less uplifting. "The morgue was at one end of the complex off hospitals, so they took the bodies out and hid them in the long grass on the side of the waste ground, to be collected on the return journey, saving them the burden of pulling their wagon full to the end of the estate. You would be taking a stroll round the grounds in the afternoon, only to come across two or three bodies laid on the waste land where eats and stray dogs made their home."

Molloy's memories of his stay several Dublin sanatoriums the Pigeon House, Rialto, Crooksling made horrifying and compelling reading. But again, it was not until I returned to Dublin that I got access to such invaluable material. Courtesy of the Gilbert Library's Dublin and Irish collection, I read several other first hand accounts of TB patients in Ireland. The Royal College of Surgeons Library provided me with medical material about the treatment of the disease. Accounts of the surgical procedures used the puncturing of lungs, the cracking open of ribs seem particularly cruel and primitive to the lay reader.

Meanwhile, back in Italy, I knew none of this. So, faced with "the blank page and my own terrifying ignorance, I had to rely on instinct. I reasoned that a sanatorium would be like a cross between a prison and a hospital were not free to discharge They were regarded by the "outside" world as a sources of fear and dread and so they were locked away. Many patients were I shunned by their families and drowned by their communities.

Like most adults, I have been in hospital so far, I've avoided prison. In the end I did what every writer has to do. Reader, I invented.

The subsequent research I did, on my return to Ireland only fleshed out what I had already imagined. Much of the information I garnered did not end up in the novel at all. I did not visit any hospitals that had been sanatoriurns (except to have the photograph accompanying this article taken). Call it superstition. Or perhaps I did not want the facts in the shape of bricks and mortar getting in the way of what I'd created.

In deference to the sources quoted here, I must declare that the sanatorium in Mother of Pearl is very much a sanatorium of the imagination. I was aiming for an emotional authenticity about the kingdom of the sick rather than the strict verisimilitude of social documentary. Irene's experiences as described are as much about the dark side of life, as they are about tuberculosis. And the sanatorium is merely a microcosm of the world in which there are so many wounded outcasts.