One hundred gallons of blood is more than 75 times as much blood as is circulating through the average adult human's body at any given moment. For 84-year-old Harold Mendenhall of Riviera Beach in southeast Florida, that's the astoundingly enormous amount of the platelets he has donated throughout his lifetime.

Mendenhall, a 183-pound O-positive universal donor, donated blood for the first time in 1977 after his wife Frankie was diagnosed with breast cancer, reported the The Palm Beach Post.

His wife died seven years later, and Mendenhall resolved to continue donating blood in order to cope. Even after the devastation of losing two of his five children to disabilities in middle age, Mendenhall kept up an average of six gallons a year.

As of last month, Mendenhall has donated a full 100 gallons of blood platelets over the course of 400 donations in the past 36 years - enough to fill the gas tanks of eight Honda Civics, notes The Palm Beach Post, or the top shelves of 10 refrigerators.

"For some reason, I'm still here and I'm grateful. That's one of the reasons I keep donating," said Mendenhall to The Palm Beach Post.

Donating Blood Platelets

Mendenhall donates platelets, which are small, flat cells that help blood clot. Platelets are much more useful than whole blood in donations intended for patients with blood disorders, like those who have leukemia or have had bone marrow transplants.

One platelet donation can be worth from 12 to 18 whole blood donations, according to the American Red Cross.

In a process called platelet apheresis, blood is drawn from a donor's arm through a cell-separating machine, which collects the platelets and then returns the rest of the blood contents to the donor's body along with saline solution. The platelet donation process typically takes 70 to 90 minutes.

While whole blood donations require a waiting period of two months before someone can donate again, healthy people can provide platelet donations up to 24 times a year. Mendenhall donates as much as possible - as least once every two weeks.

Harold Mendenhall poses with One Blood staff after donating 100 gallons of blood platelets. [OneBlood - Facebook]

"Giving blood can only be done by a human being, so that's been my payback for my career and my good health and all the blessings I've had," said Mendenhall, who helped develop the engines of SR 71 Blackbird spy planes used throughout the Cold War, to The Palm Beach Post.

"He has got to be the nicest, most generous person I know," said Frankie Groover, who helps run the platelets division at the One Blood center in Lake Park, Florida.

Mendenhall told The Palm Beach Post that donating 100 gallons of blood platelets over the past decades has helped him stay on top of his own health care, since the phlebotomists at One Blood monitor his vital signs and test for blood-borne diseases at each visit.

"It's like getting a check-up every two weeks," said Mendenhall.

Harold Mendenhall receives an award from One Blood for donating 100 gallons of blood. [Facebook / OneBlood]

Source: The Palm Beach Post