On 2nd day of hospitalization, each volunteer receives an oral dose of DS. Over the next 24 hours, 15 blood samples are obtained (from 15 separate needle sticks). On 4th day, each volunteer is given an injection of DS into vein. 18 blood samples are obtained. Blood is withdrawn before the infusion, at the end of the infusion, and 30 and 60 minutes after the infusion. All urine is collected.