The next step was to test insulin in humans. So on 11 January 1922, insulin was administrated to Leonard Thompson a 14-year-old boy treated for diabetes in Toronto Hospital[13]. It’s worth mentioning that after the introduction of Apollinaire Bouchardat’s (1806-1886) pioneering dietary treatment for diabetes, physicians repeated in several generations of diabetics his motto: “mangez le moins possible” (eat as little as possible)[21,22]. Thomson was also following a strict fasting diet proposed by Frederick Madison Allen (1879-1964) and he was in critical state. He received 15 mL of insulin, injected in his buttock but he developed abscesses at the injection site and became even sicker. Collip further improved the quality of insulin and on January 23, Thompson received a second injection. The results were excellent. His blood glucose from 520 mg/dL fell to 120 mg/dL in 24 h and urinary ketones disappeared. Thompson continued the treatment with insulin and lived another 13 years. He died of pneumonia at 27 years old[13].