"It's one of my talents, probably my only talent, is that I can be a blood donor".
More than three million doses of Anti-D containing Mr Harrison's blood have been given to Australian mothers with a negative blood type since 1967.
He's known, unsurprisingly, as "the man with the golden arm".
Each week, the "man with the golden arm", as people call the 81-year-old, has donated 500-800ml of blood plasma.
Since 1976, Harrison's blood has been used in more than 3 million injections given to Rh-negative Australian women, the organization says.
"His body produces a lot of them and when he donates his body produces more".
"In Australia, up until about 1967, there were literally thousands of babies dying each year, doctors didn't know why, and it was very bad", explains Jemma Falkenmire, of the Australian Red Cross Blood Service.
Jemma Falkenmire, spokesperson for the Blood Service, said: "Every bag of blood is precious, but James' blood is particularly extraordinary".
On Friday, after more than 60 years and 1173 donations, Harrison made his final benefaction.
'Women were having numerous miscarriages and babies were being born with brain damage.
The medicine, anti-D, is given to pregnant mothers whose rhesus negative blood is at risk of attacking her baby's rhesus positive blood.
Rhesus disease does not harm the mother, but it can cause the baby to become anaemic and develop jaundice (yellowing of the skin and whites of the eyes).
Harrison did not hesitate when he was asked to join the Anti-D program.
"I hope it's a record that somebody breaks, because it will mean they are dedicated to the cause", Mr Harrison said of his last donation. He retires with 1162 donations from his right arm and 10 from his left. The Australian researchers realised that they could combat HDN by using Anti-D injections, so Harrison switched over to make blood plasma donations to help people.
"It becomes quite humbling when they say, 'oh you've done this or you've done that or you're a hero, '" Harrison said.
Harrison has now passed the Australian Red Cross's donor age limit, but he told the Sydney Herald he'd "keep on going if they'd let me".
Beth Ismay had four Anti-D injections during her second pregnancy with daughter Layla. The anti-D doesn't pass to the fetus, however, keeping both mother and fetus safe.
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. Only 160 donors support the program, and finding new donors has proven to be hard.
Attempts to create a synthetic version has so far failed.
The condition develops when a pregnant woman has rhesus-negative blood (RhD negative) and the baby in her womb has rhesus-positive blood (RhD positive), inherited from its father.
When he was 14, Harrison underwent a major chest surgery, receiving blood transfusions that saved his life, according to a statement published by Australian Red Cross Blood Service website.
"It really is the gift of life".