In an experiment to determine the effect of a drug on the blood glucose concentration of diabetic rats, six rats were given the drug while five others were used as controls. The blood glucose levels of the treated group (in mg/ml) were 2.02, 1.71, 2.04, 1.50, 1.83, and 1.64; for the controls, the levels were 2.15, 1.92, 1.78, 2.04, and 2.22. Assuming these samples come from normal distributions with the same standard deviation, test the hypothesis that the treatment has no effect on mean blood glucose concentration.