"It’s a sad day for me. The end of a long run," Mr Harrison says as his blood flows from the crook of his right arm to the plasmapheresis machine at the Town Hall Donor Centre in Sydney. When a pregnant woman with an Rh negative blood type is carrying a baby with Rh positive blood, her body registers the baby’s red blood cells as a foreign threat (an invading virus or bacteria) and produces antibodies to destroy the invader. The effects can be devastating. The disease causes multiple miscarriages, still births, and brain damage or fatal anaemia in newborns. James Harrison, surrounded by mothers of Anti-D babies at his final donation. (from left to right): Christine Damiandis and Georgio, Michelle Dibbs and Eloise, Tanya McLaren and Brianna, Sarah Doyle and Grace. Credit:Steven Siewert HDN killed thousands of Australian babies every year before Austrtalian scientists made a breakthrough discovery in the 1960s.

Illustration: John Shakespeare They realised they could head off HDN by injecting Rh- mothers with low levels of donated RhD immunoglobulin. The antibodies mop up any Rh+ blood cells of without harming the baby. The very first mother received her dose of Anti-D at Royal Prince Alfred Hospital in 1967. Mr Harrison produces the rare combination of RhD-negative blood and Rh+ antibodies naturally, making him the ideal donor. "Every ampule of Anti-D ever made in Australia has James in it," said Robyn Barlow the Rh program co-ordinator who recruited Mr Harrison, the program's first donor.

"It’s an enormous thing ... He has saved millions of babies. I cry just thinking about it," she said. Jemma Falkenmire at the Australian Red Cross Blood Donor Service said: "Very few people have these antibodies in such strong concentrations. "His body produces a lot of them and when he donates his body produces more," she said. He has saved millions of babies. I cry just thinking about it. Robyn Barlow Scientists suspect this has something to do with the 13 units of blood transfusions he received after undergoing major chest surgery when he was 14.

Mr Harrison did not hesitate when he was asked to join the Anti-D program in its very early phase. It was his way of giving back after receiving his own life-saving transfusion. "They asked me to be a guinea pig, and I've been donating ever since," Mr Harrison said. "I'd keep on going if they'd let me," Mr Harrison said. But he has already surpassed the donor age limit and the blood service made decision to protect his health. HDN still has the potential to affect one in six newborns in Australia. Roughly 17 per cent of pregnant women receive Anti-D, including Mr Harrison’s own daughter. They asked me to be a guinea pig, and I've been donating ever since. I'd keep on going if they'd let me. James Harrison

Roughly 17 per cent of pregnant women receive Anti-D injections in Australia. The blood service calculated that Mr Harrison has helped prevent 2.4 million deaths by analysing national birth data since 1964 and the proportion of the population that received Anti-D and the HDN mortality risk. Almost every week, Mr Harrison - dubbed "the man with the golden arm" - has donated 500-800ml of blood plasma. He retires with 1162 donations from his right arm and 10 from his left. Almost all of his donations have come from his right arm: the golden limb. "It could be all in the brain, but I can feel it in the left arm when they inject, so I've only had ten in my left. I don't feel it in my right arm.

He never watches the needle go in when he turns up for his weekly blood plasma donation at Australian Red Cross clinics. "I look at the nurses, the ceiling, the spots on the wall, anything but the needle. It's too macabre, I think; watching yourself get stuck with the needle." 'He really is remarkable' Loading Mr Harrison draws out the process of his final donation as he reclines in a chair, squeezing a firm sponge absent-mindedly and enjoying the gaggle of half a dozen Anti-D babies cooing in their mothers' arms; families who have come to thank him on his last day.

Beth Ismay had four Anti-D injections during her second pregnancy with daughter Layla. "He really is remarkable," Ms Ismay says, "keeping our babies safe." Ms Barlow agrees. "We’ll never see his kind again ... that he has been well and fit and his veins strong enough to continue to donate for so long is very, very rare," she said. Australia’s Anti-D program is wholly dependent on just 160 donors. Recruiting new donors is a laborious task. Attempts to create a synthetic version has so far failed. The blood service recently started a three-year research project to harvest Mr Harrison’s DNA and create a library of his monoclonals – the cocktail of antibodies and white blood cells that herald a promising new phase in the Anti-D program.