The purpose of an experiment is to investigate the effect of vagal nerve stimulation on insulin secretion. The subjects are mongrel dogs with varying body weights. Table E7.2 gives the amount of immunoreactive insulin in pancreatic venous plasma just before stimulation of the left vagus and the amount measured 5 minutes after stimulation for seven dogs. Test the null hypothesis that the stimulation of the vagus nerve has no effect on the blood level of immunoreactive insulin; that is,