Glands regulate distant parts of the human body with hormones. The pancreas regulates the body with a hormone called insulin. A biologist wanted to discover the effects of insulin from the pancreas. The biologist altered the pancreases from 30 mice. The biologist kept another 30 mice unaltered. Then the biologist recorded the differences that developed between the mice in both groups. What method did the biologist perform to investigate the role of the pancreas?