Frederick Banting’s discovery of insulin in the 1920s saved a child’s life. It’s still saving lives.

In the 1800s, the life expectancy for a 10-year-old child with Type 1 diabetes was about one year. Now people with Type 1 diabetes can expect to live around 68 years on average. One big reason why: the discovery of the hormone insulin by a team led by Frederick Banting, an early-20th-century scientist from Canada, which revolutionized treatment for the disease. Today, we celebrate Banting’s 125th birthday with a Google Doodle in his honor and with World Diabetes Day.

Diabetes is one of the first human diseases on record. Ancient Egyptian manuscripts from as far back as 1500 BC mention a disease “characterized by the ‘too great emptying of urine.’” Around 500 BC, an Indian physician described patients with urine so sweet and sticky it attracted ants.

These ancient reports were likely of Type 1 diabetes, the autoimmune version of the disease where antibodies damage the cells in the pancreas that secrete insulin. Insulin is the hormone responsible for taking sugar out of the bloodstream and transferring it into the body’s cells, where it can be used for energy.

When the body stops making insulin, blood sugar rises. And unchecked high blood sugar can lead to a range of complications — from deteriorating eyesight to nerve damage to the buildup of chemicals called ketones in the blood. Ketones at high levels can be poisonous, causing the blood to turn acidic.

(In Type 2 diabetes, the pancreas still produces insulin, but the body has become resistant to its effects. It’s a metabolic disease, rather than an autoimmune disease.)

While ancient physicians recognized that the disease was a result of mismanagement of the body’s sugar, they didn’t know what caused it. (Doctors still don’t know what, exactly, causes Type 1 diabetes.) But they knew if there was a way to reduce the body’s blood sugar level, symptoms might improve.

One clue to how to treat Type 1 diabetes came in 1889, when German physicians Oskar Minkowski and Joseph von Mering discovered that removing the pancreas of dogs caused the animals to develop severe and fatal diabetes. In the following years, scientists tested: What was it about the pancreas that kept the blood’s sugar in balance?

In the early 1920s, Banting and his colleague Charles Best thought they had finally identified the right enzyme, and in experiments took pains to make sure it did not come into contact with caustic digestive chemicals. It’s said Banting and Best first injected the substance into themselves, soon noticing it caused a drop in their blood sugar. They then took their serum and injected it into dogs with diabetes.

The solution “invariably caused a marked reduction in blood sugar and in the amount of sugar excreted in the urine,” Banting and colleagues announced in the Canadian Medical Association Journal in 1922.

The substance in Banting’s serum was insulin. And in short time, it was tested on a human, a dying 14-year-old boy named Leonard Thompson.

Thompson, a patient at a Toronto hospital, was not doing well. Back then, the recommended treatment for Type 1 diabetes was a near-starvation diet (in the hopes that eating as little as possible would keep sugar from accumulating in the blood). Thompson was a frail 65 pounds, and wasn’t expected to live much longer. After two rounds of insulin injections, Thompson’s blood sugar levels had stabilized. He lived until age 27 (when he died of pneumonia).

In those early days, insulin was produced from animals. Synthetic insulin (the hormone that exactly mirrors the human hormone) wasn’t manufactured until the 1960s, when genetic engineering made it possible for bacteria to produce the chemical.

But by 1923, insulin was commercially available. That same year, Banting and John James Rickard Macleod were awarded the Nobel Prize in Physiology or Medicine for the discovery. (Banting felt Best should have been credited for the discovery, not Macleod, who held more of a supervisory role.)

“Although insulin doesn’t cure diabetes, it’s one of the biggest discoveries in medicine,” the Nobel Prize website reads. “When it came, it was like a miracle.” And to this day, it still saves millions of lives. By injecting insulin multiple times a day, people with Type 1 diabetes can control their symptoms.

That said, there are still obstacles to Type 1 diabetes care: It’s a constant challenge to keep up the injections and blood sugar monitoring throughout the day. People with diabetes are still holding out for a true “artificial pancreas,” which would automate the diagnostic monitoring and injections.

Many more advances in the spirit of Banting are still needed.