Why is Michael throwing up?

Michael's pediatrician first suggested we try giving him prevacid to see if his throwing up was caused by acid reflux.  It didn't make any difference.  So on Monday Liz took Michael to get x-rays of his stomach.  He had to drink a Barium solution and take x-rays periodically to see how the solution moved through his digestive system.  Michael threw up the initial Barium solution, but was able to keep the second round down.  The x-rays didn't show any problems with his digestive system.