This is a clinical research study to establish normal values for the infusion of a synthetic form of the hormone cholecystokinin(CCK-8) for gallbladder emptying. Cholecystokinin is released from the small bowel to stimulate the pancreas and gallbladder to help digest and absorb food. Some people have gallbladder problems and need to be tested with the synthetic cholecystokinin ( Kinevac®, Bracco Diagnostics, Inc.). The aim of this study is to find out how differing amounts and intravenous infusion times of CCK-8 affect gallbladder emptying. The findings in normal subjects will be used to establish normal values that can then be compared with patients with suspected gallbladder disease.