James Harrison did not much care for needles. Whenever he donated plasma, he would look away as the tip went into his arm.

But Mr. Harrison, an Australian who died last month at 88, was one of the most prolific donors in history, extending his arm 1,173 times. He may have also been one of the most important: Scientists used a rare antibody in his plasma to make a medication that helped protect an estimated 2.4 million babies in Australia from possible disease or death, medical experts say.

“He just kept going, and going, and going,” his grandson Jarrod Mellowship, 32, said in an interview on Monday. “He didn’t feel like he had to do it. He just wanted to do it.”

Mr. Harrison — who was affectionately known as “The Man with the Golden Arm” — died in his sleep at age 88 on Feb. 17, at a nursing home about an hour’s drive north of his regular donation center in Sydney, Mr. Mellowship said.

Mr. Harrison’s plasma contained a rare antibody, anti-D. Scientists used it to make a medication for pregnant mothers whose immune systems could attack their fetuses’ red blood cells, according to Australian Red Cross Lifeblood.

It helps protect against problems that can occur when babies and mothers have different blood types, most often if the fetus is “positive” and the mother is “negative,” according to the Cleveland Clinic. (The positive and negative signs are called the Rhesus factor, or Rh factor.)