The entire gut, including esophagus with vagus nerve trunks attached, and stomach and intestines and mesentery, is dissected and placed in a dish with oxygenated Krebs-Ringers solution. The small intestine, as well as pancreas and spleen, are removed carefully. The colon is pinned and gently flushed of its contents. The right vagus nerve trunk is gently dissected away from the esophagus. The tissue is perfused with 35-degree, oxygenated Krebs-Ringers for the duration of the experiment.